I thought about your thread today so I timed each truck setting at idle to build air at 120 psi. If your semi truck air compressor isn’t building pressure, there are a few things you can check to troubleshoot the issue. Q: Does the governor control the air compressor?. The truck running is too noisy to. When truck is running I rev the motor to 2K and can only build air pressure to 70 PSI ish, before fan cuts out then pressure stops building, when released the air pressure starts to drop in both the (F) and (R) tanks. 439 views, 51 likes, 12 loves, 73 comments, 19 shares, Facebook Watch Videos from Sibya TV: SibyaTV: Balita / May 5, 2023 Lunes hangtud Byernes kauban. We replace very few air compressors. build air pressure at idle. These faults will both keep the compressor from kicking in and the door fault will cause your concern. The SPN 3984 is for a mode door stuck on the HVAC unit. Both air gauges stay still for minutes at a time. Air Compressor and Air System Pressure - You should be aware of common air pressure thresholds of your motorcoach’s brake system. Truck has hydraulic brakes but air for ebrake. Common Red Flags of a Faulty Air Compressor: Truck not building air pressure. (If the vehicle has larger than minimum air tanks, the buildup time can be longer and still be safe. dumps the unloader signal and allows the air compressor to build air pressure. when i start truck air pressure builds slowly takes about 20 min to build but after it gets past 90psi seems to build as should. However, the exact pressure varies between truck models and state laws. Truck has hydraulic brakes but air for ebrake. They are easy to replace, just a little length to explain. Make sure there is no oil or water in the signal line, That can destroy an air governor in no time. The air is stored in a series of pressure tanks on the truck. Start the engine and watch the air pressure gauges climb to 120-135 psi, and if they keep rising past that pressure, the governor is faulty. Have you ever had issues with your truck not building air pressure? Heres how to troubleshoot the issue! Show more Show more Air wont build tap air dryer purge valve Double D Distribution. The governor will either be mounted on the side of the air compressor or air dryer. How long should a truck take to build air pressure? – Short. The secondary pressure … read more Wayne Journeyman Vocational, Technical or Tra 5,816 satisfied customers Air in secondary tank will not build air over 50psi at idle. These tests are to check if the governor can put the compressor in the load and unload phase. Air Pressure Building Up to 150 PSI and not releasing>Air Pressure Building Up to 150 PSI and not releasing. My secondary air gauge isn’t building pressure. 8K views, 286 likes, 28 loves, 28 comments, 48 shares, Facebook Watch Videos from Uriah Hickman: Saudi Arabia & Egypt JUST Joined. When i start truck air pressure builds slowly takes about 20 when i start truck air pressure builds slowly takes about 20 min to build but after it gets past 90psi seems to build as should. dumps the unloader signal and allows the air compressor to build air pressure. HELP, building too much air!. Semi Truck Not Building Air Pressurewhy Air Pressure not building up on semi truck ? (Best Solution) - YouTube 0:00 / 12:21 HOUSTON why Air Pressure not building up on semi truck ? (Best Solution) 25,664 views Apr 19,. The air is stored in a series of pressure tanks on the truck. I recently had slack adjusters done if that means anything. The compressor must raise the air systems pressure using maximum engine rpm, from 85 psi to 100 psi within the time calculated: Actual reservoir capacity x 25 / required reservoir capacity. Once the pressure in the wet tank reaches 125-130 psi the air gov. This is a diagnostic procedure of when your truck will not build any air pressure at all. This is a diagnostic procedure of when your truck will not build any air pressure at all. If the governor is plumbed correctly the unloader valve may be stuck in the air compressor head or the wet tank/signal line could be plugged. its slow about building air. If everything builds and works as it should then I would replace the compressor. Air in secondary tank will not build air over 50psi at idle … read more Expert. The governor will either be mounted on the side of the air compressor or air dryer. So this is a sort of procedure. The duty cycle is the ratio of time the compressorspends building air to the total engine running time. Just put a new air dryer I got from Volvo but did not solve the problem. The higher the pressure, the heavier the load the tire can support. Look for small leaks first ,Second bypass air drier (to try ),Third replace govenor ,Fourth replace unloaders in compressor ,Last replace compressor. Air compressors typically have a “cut-out” pressure between 110 psi and 130 psi and a “cut-in” pressure about 20 psi lower. Then, throttle your truck a bit and notice if the needles are. Symptoms Of a Bad Air Governor – Cause and Fixes – Rx Mechanic. As you consume air and the pressure drops towards 100, before the beginning of the charge cycle I get a ticking noise. The cut-out pressure for an air governor depends on the settings, but it should be roughly 30 psi higher than the pressure when the air compressor engages, which is 90 psi, so the cut-out pressure should be set at 120 psi. adequacy of the air system. It will not build pressure if the exhaust is open, but rather pass the air through. 1 note the air pressure remaining in the tractor’s air systems (should be at least 20 psi). At low damage levels (below 10%) you shouldnt be having any problem with air pressure overnight. Note: Be careful not to over adjust. Subject: RE: Cold truck wont build air So. Try using shop air to manually air up your system through the primary tank during troubleshooting to make it easier when disconnecting your airlines and looking for restrictions. The air pressure gauge tells you the. The only way to build up air is to start driving it and about 5 or so minutes of driving- pressure is all the way up and everything is working properly! Im thinking the air governor might need to be replaced but can that also be the cause of loss of air in mere 7-8 hours? Thank for the help guys! R SpankingGT, Dec 26, 2011 #1 + Quote Reply. When i start truck air pressure builds slowly takes about 20 when i start truck air pressure builds slowly takes about 20 min to build but after it gets past 90psi seems to build as should. The pressure is regulated by the air governor on the air compressor. This discussion is proudly sponsored by: Please support our sponsors and let them know you heard about their products on iRV2 Thread Tools. why Air Pressure not building up on semi truck ? (Best Solution) - YouTube 0:00 / 12:21 HOUSTON why Air Pressure not building up on semi truck ? (Best Solution) 25,664 views Apr 19,. Air Pressure Building Up to 150 PSI and not releasing. Or, it may seem to be building pressure more slowly than normal. Utilize 120-130psi pressure on the discharge port and put soap on the. The governor will either be mounted on the side of the air compressor or air dryer. Air operated PTO systems do not work until you reach 90psi. Wont build pressure above 30 psi. Dan : Sounds like you might have a restriction in either the fittings or the check valves at the tanks. When i start truck air pressure builds slowly takes about 20 when i start truck air pressure builds slowly takes about 20 min to build but after it gets past 90psi seems to build as should. Already checked read more BrentR718 14 satisfied customers 98 Pete n 14 select. 43 (a) Every motor vehicle, if used to tow a trailer equipped with brakes, shall be equipped with means for providing that in case of breakaway of. Even though the compressor motor might shut down due to it having a thermal cut-off switch, overheating the motor is never good. Sounds coming from safety valves. Common Red Flags of a Faulty Air Compressor: Truck not building air pressure. Air pressure goes over 145. Inspect air lines to and from governor tor kinks and restrictions. Air dryer purges at 120 or so and the truck holds air fine. You have realistic air brake system enabled. BTW on newer trucks governor may be integrated to air processing unit (air governor + air dryer + four vay protection valve Fist I do if compressor overbuilds air - I remove unloader line from compressor and check does it blows air if pressure goes over 125-140 PSI, if yes - stuck unloader, if not - bad governor Pablo-UA, Jul 11, 2014. Wont build pressure above 30 psi iRV2. its slow about building air. Once the air pressure drops a certain point in the wet tank, the air gov. Start the vehicle engine and build up air pressure in the air brake system and check the pressure registered by a dash or test gauge at the time the governor cuts-out, stopping the compression of air by the compressor. You have realistic air brake system enabled. Bendix Air Compressor How to & Troubleshooting Guide. Air operated PTO systems do not work until you reach 90psi. Apply liquid soap to the inlet port and apply 120-130psi of pressure to the unloader. The air pressure is building up to 150 PSI and not releasing. Dan : Click here for an example of one style check valve. Check that it takes no longer than 2 minutes for air pressure to rise from 85. You can try tapping on the side of it to see if the truck will build air. How to keep air brakes working in cold weather conditions. Best way I found to confirm this is to remove the discharge line from the compressor (when engine is cooled down) and supply air pressure to system with shop air pressure. When truck is running I rev the motor to 2K and can only build air pressure to 70 PSI ish, before fan cuts out then pressure stops building, when released the air pressure starts to drop in both the (F) and (R) tanks. Mechanic has had it for two days and said its not air dryer or regulator. but will up if I rev up rpm to alittle over 1500. Inspect air lines to and from governor tor kinks and restrictions. Any ideas? He is willing to say he cannot fix it and send me on my way. Rear Brake Reservoir Excessive oil or water accumulaUon Loses air pressure · Safety Valve Pops off at 150 PSI Pops off below 150 PSI Will not function. Air compressors are designed to build air (run “loaded”)up to 25% of the time. Q: Does the governor control the air. First, make sure that the air compressor is turned on and that there is power running to it. When the truck is running it loses about 5psi per minute secondary air and the air compressor will not load until the. Then, throttle your truck a bit and notice if the needles are climbing. and secondary tank wont hold over 90psi while driving & will drop to 60 psi at idle I have a 2003 International 9200i tandem semi tractor. If they do, then you can be sure that the compressor is in the load phase. load capacity, you need at least 6,600 lb. It will not build pressure if the exhaust is open, but rather pass the air through. When proper adjustment is obtained, tighten the adjusting screw locknut and replace the cover. Best way I found to confirm this is to remove the discharge line from the compressor (when engine is cooled down) and supply air pressure to system with shop. 2015 … read more Mike Mcmillan Triage Tech/Shop Foreman Associates 624 satisfied customers I have codes 4811 fmi 2 can you tell me whats the problem. Have you ever had issues with your truck not building air pressure? Heres how to troubleshoot the issue! Show more Show more Air wont build tap air dryer purge. The secondary air pressure is dropping with the depression of the service brake pedal. Higher duty cycles causeconditions that affect air brake charging systemperformance which may require additionalmaintenance. An air compressor that will not build pressure runs on long past the point where it normally would reach the cut-out pressure level and stop. Make sure the minimum operating pressure for a vehicle air-brake system is no less than 100 psi for a truck. If air pressure does not build up fast enough, the pressure may drop too low during driving, requiring an emergency stop. Have a 06 frieghtliner m2 Mercedes engine, having a problem getting the air pressure up past 50-55. Best way I found to confirm this is to remove the discharge line from the compressor (when engine is cooled down) and supply air pressure to system with shop air pressure. The duty cycle is the ratio of time the compressorspends building air to the total engine running time. When i start truck air pressure builds slowly takes about 20. You’re safer going a bit above the minimum, say 6,945 lb. Wont build air pressure past 50??. The reservoir port goes to the wet tank, the unloader goes to the air compressor unloader and the air dryer purge. M939 Air system Diagnostics. If unloader stems are worn, replace. To understand inflation pressure, you have to understand that it’s not the tire itself that supports the load, but the air inside the tire. Truck Not Building Air Pressure? Fix This Problem Today!. Basically dash guage will fill slowly to 50, wont go above that unless i rev it to about 1500 rpm. If your semi truck air compressor isn’t building pressure, there are a few things you can check to troubleshoot the issue. Air Compressor and Air System Pressure - You should be aware of common air pressure thresholds of your motorcoach’s brake system. An air compressor that will not build pressure runs on long past the point where it normally would reach the cut-out pressure level and stop. You also didnt mention hearing a leak. So if you have an air switch the gear will not seat until that pressure is reached. Have a 06 frieghtliner m2 Mercedes engine, having a problem getting the air pressure up past 50-55. These tests are to check if the governor can put the compressor in the load and unload phase. How fast should a semi truck build air pressure? 85 to 100 psi Quote From The CDL Manual: Check rate of air pressure buildup: When the engine is at operating RPM, the pressure should build from 85 to 100 psi within 45 seconds in dual air systems. ) Note: This is a requirement at the time of manufacturing. A FAW semi-trailer truck in China. Plumb in a fitting from your shop air compressor ,Then you can find the small leaks. You can see stamped on the sidewall the maximum pressure for any tire. Wont build pressure above 30 psi iRV2. install it in compressor output hose. 2015>My secondary air gauge isn’t building pressure. GMC with Detroit & hendrixson suspension took 4 minutes,so did my Peterbilt tractor. SPN 2609 FMI 16-- HVAC High Pressure Protection head Pressure exceeded 480 psi Compressor will shut off. You can try tapping on the side of it to see if the truck will build air. The compressor must raise the air systems pressure using maximum engine rpm, from 85 psi to 100 psi within the time calculated: Actual reservoir capacity x 25 / required reservoir capacity. A semi-trailer truck, also known as a semitruck, [1] (or semi, [2] eighteen-wheeler, [3] big rig, [4] tractor-trailer [5]) [6] [a] is the combination of a tractor unit and one or more semi-trailers. Air compressor wont stop building air. The air pressure is building up to 150 PSI and not releasing. equipped with air brakes, a system to protect the air pressure in the towing vehicle from effects of a loss of air pressure in the towed vehicle. Look around your air tank for any type of rust around any of the straps, etc. An air governor on the compressor. (If the vehicle has larger than minimum air tanks, the buildup time can be longer and still. Once the air pressure. The Russians have destroyed Three Ukrainian Armies. Pull them off and clean them out. Look for small leaks first ,Second bypass air drier (to try ),Third replace govenor ,Fourth replace unloaders in compressor ,Last replace compressor. The air is pressurized by the air compressor on the truck’s engine. Too much pressure building up. Then come a different set of drones that literally fly right into those pieces of equipment and disabled them. Vocational, Technical or Tra 3 satisfied customers. Air pressure will not build upwas in sleeper when. The higher the damage level on your truck, the faster you lose air pressure. If this never happens then you have a bad air governor. Have a 06 frieghtliner m2 Mercedes engine, having a problem getting the air pressure up past 50-55. The air governor has 3 ports-unloader, exhaust and reservoir. Check that it takes no longer than 2 minutes for air pressure to rise from 85. Sounds like the compressor stopped building pressure. The only way to build up air is to start driving it and about 5 or so minutes of driving- pressure is all the way up and everything is working properly! Im thinking the air governor might need to be replaced but can that also be the cause of loss of air in mere 7-8 hours? Thank for the help guys! R SpankingGT, Dec 26, 2011 #1 + Quote Reply. You might have sludge or carbon buildup Customer: right on, thanks for the help. adequacy of the air system. This is a diagnostic procedure of when your truck will not build any air pressure at all. Make sure the minimum operating pressure for a vehicle air-brake system is no less than 100 psi for a truck. You can see stamped on the sidewall the maximum pressure for any tire. The cut-out pressure should be in accordance with the pressure setting of the piece number being used. While driving, observe the air pressure gauge during build-up to ensure proper air system operation. air pressure :: American Truck Simulator General Discussions>air pressure :: American Truck Simulator General Discussions. And then if thats not enough, rocket artillery rains down on whats there and kills everyone. Air pressure build-up from 85 psi to 100 psi should take 45 seconds or less. These tests are to check if the governor can put the compressor in the load and unload phase. If not released, release the tractor parking brakes, Note: Federal. The secondary pressure read more Wayne Journeyman Vocational, Technical or Tra 5,816 satisfied customers Air in secondary tank will not build air over 50psi at idle. sends an air signal to the air compressor unloader and dryer purge port. OR will not build air pressure above a certain PSI - like 40 or 60psi. 1 Air compressor cut-in pressure requires that the governor cut-in pressure is at least 85 psi for a bus and at least 100 psi for a truck. 4 Pressure gauge requires a pressure gauge that is visible to the driver for each service brake system. Federal Motor Vehicle Safety Standards No. If your semi truck air compressor isnt building pressure, there are a few things you can check to troubleshoot the issue. The cut-out pressure for an air governor depends on the settings, but it should be roughly 30 psi higher than the pressure when the air compressor engages, which is 90 psi, so the cut-out pressure should be set at 120 psi. Subject: RE: Cold truck wont build air So. It sounds like it happened fairly quickly. Federal Motor Carrier Safety Administration>Table of Contents. Now the W-900 wrecker took 8 1/2 minutes to air up,But it also has …. The air is pressurized by the air compressor on the trucks engine and then stored in a series of pressure tanks on the truck. AIR BRAKE SYSTEM TROUBLESHOOTING I. Make sure the minimum operating pressure for a vehicle air-brake system is no less than 100 psi for a truck. Air Governor – Cause and Fixes – Rx Mechanic>Symptoms Of a Bad Air Governor – Cause and Fixes – Rx Mechanic. Both of these concerns could point to. Shut off the engine and drain all air pressure from the vehicle. Have a 06 frieghtliner m2 Mercedes engine, having a problem getting the air pressure up past 50-55. Rear Brake Reservoir Excessive oil or water accumulaUon Loses air pressure · Safety Valve Pops off at 150 PSI Pops off below 150 PSI Will not function. air pressure :: American Truck Simulator General Discussions. Air Compressor and Air System Pressure - You should be aware of common air pressure thresholds of your motorcoach’s brake system. Air compressors typically have a “cut-out” pressure between 110 psi and 130 psi and a “cut-in” pressure about 20 psi lower. I have attached the motor and air compressor with soap water and found nothing for leaks, also attached the governor mounted on. Do not drive until you get the problem repaired. First, you must pump it down to above 80 psi. Plumb in a fitting from your shop air compressor ,Then you can find the small leaks. The governor will either be mounted on the side of the air compressor or air dryer. Start the vehicle engine and build up air pressure in the air brake system and check the pressure registered by a dash or test gauge at the time the governor cuts-out, stopping the compression of air by the compressor. com FAQ Mark Forums Read Mission Statement: Supporting thoughtful exchange of knowledge, values and experience among RV enthusiasts. james Roberts. Truck has hydraulic brakes but air for ebrake. Test air leakage rate: With a fully-charged air system (typically 125 psi), turn off the engine, release the parking brake, and time the air pressure drop. BTW on newer trucks governor may be integrated to air processing unit (air governor + air dryer + four vay protection valve Fist I do if compressor overbuilds air - I remove unloader line from compressor and check does it blows air if pressure goes over 125-140 PSI, if yes - stuck unloader, if not - bad governor Pablo-UA, Jul 11, 2014. Look around your air tank for any type of rust around any of the straps, etc. Advanced Troubleshooting Guide for Air Brake Compressors. Fast cycling from the wet tank. There should be no air psi on this line until at least 120 psi (depends where the air governor is set). OR will not build air pressure above a certain PSI - like 40 or 60psi. It will not build pressure if the exhaust is open, but rather pass the air through. IL We always pull the outline on the compressor thats usually the flex hose and dump in some alcohol, if that dont work then get some heat under the truck with portable heaters and use some cardboard to hold the heat under the truck. Here are some steps to take before heading out on the road: Make sure the minimum operating pressure for a vehicle air-brake system is no less than 100 psi for a truck. that might be leaking and causing the tank not to build pressure. Tthat leaves you little margin. truck wont build air>Viewing a thread. Mechanic has had it for two days and said its not air dryer or regulator. build air pressure>Viewing a thread. If your pump smoked, then you probably melted the o-rings in that shaft that you manually pushed in. Gear turns the pump which pushes the fluid. OR will not build air pressure above a certain PSI - like 40 or 60psi. Air pressure goes over 145. The air pressure gauge tells you the adequacy of the air system. equipped with air brakes, a system to protect the air pressure in the towing vehicle from effects of a loss of air pressure in the towed vehicle. The higher the pressure, the heavier the load the tire can support. Each 1/4 turn of the adjusting screw raises or lowers the pressure setting approximately 4 psi. While driving, observe the air pressure gauge during build-up to ensure proper air system operation. Jason the mechanic: Air brakes and the simple explanation. Air Brake Systems for Truck, Bus & Tractor 4 Federal Regulations Compressors & Governors Compressor Performance: 49CFR571. The only way to build up air is to start driving it and about 5 or so minutes of driving- pressure is all the way up and everything is working properly! Im thinking the air governor might need to be replaced but can that also be the cause of loss of air in mere 7-8 hours? Thank for the help guys! R SpankingGT, Dec 26, 2011 #1 + Quote Reply. A load-range G is typically 105 psi, whereas a load-range H is 120 psi. The secondary air pressure is dropping with the depression of the service brake pedal. This is a diagnostic procedure of when your truck will not build any air pressure at all. Subject: RE: Freightliner wont build air pressure If nothing on a line, connection, or fitting comes up, drop some soapy water down along the outer face of the frame rails where the tanks mount. Once that pressure has been reached then there should be air pressure (same as system psi). Air dryer will not purge. If you’re inflating your drive and trailer tires to 100 psi, they are probably over inflated. New Member. Subject: RE: Freightliner wont build air pressure If nothing on a line, connection, or fitting comes up, drop some soapy water down along the outer face of the frame rails where the tanks mount. The truck running is too noisy to hear an air leak. bulldozerbert Posted 2/11/2016 10:38 (#5103814 - in reply to #5103807). What Causes a Truck Not Building Pressure? When having a truck not building air pressure, it is usually because the unloader valve is stuck. adequacy of the air system. I have a 1995 Ford LTL9000 Aeromax. Trickiest leak we ever found was due to the fact that one air tank was very close to the frame rail. We replace very few air compressors. Have you ever had issues with your truck not building air pressure? Heres how to troubleshoot the issue! Show more Show more Air wont build tap air dryer purge valve Double D Distribution. Air in secondary tank will not build air over 50psi at idle read more Expert. air pressure problem need help, 2004 volvo vnl 780. Just remove the shaft and put new o-rings on. com Heavy Duty Replacement Truck Parts. Jason the mechanic: Air brakes and the simple explanation>Jason the mechanic: Air brakes and the simple explanation. Make sure that any leaks are not above 50sccm. The air pressure is building up to 150 PSI and not releasing. why Air Pressure not building up on semi truck ? (Best Solution) - YouTube 0:00 / 12:21 HOUSTON why Air Pressure not building up on semi truck ? (Best Solution) 25,664 views Apr 19,. Air compressors typically have a cut-out pressure between 110 psi and 130 psi and a cut-in pressure about 20 psi lower. sends an air signal to the air compressor unloader and dryer purge port. Inspect air lines to and from governor tor kinks and restrictions. To understand inflation pressure, you have to understand that it’s not the tire itself that supports the load, but the air inside the tire. Wont build air pressure at idle. The result is the compressor motor will overheat. Already checked … read more BrentR718 14 satisfied customers 98 Pete n 14 select. In single air systems (pre-1975), typical requirements are pressure buildup from 50 to 90 psi within 3 minutes with the engine at an idle speed of 600-900 rpms. The cut-out pressure for an air governor depends on the settings, but it should be roughly 30 psi higher than the pressure when the air compressor engages, which is 90 psi, so the cut-out pressure should be set at 120 psi. Start the engine and watch the air pressure gauges climb to 120-135 psi, and if they keep rising past that pressure, the governor is faulty. Have you ever had issues with your truck not building air pressure? Heres how to troubleshoot the issue! Show more Show more Air wont build tap air dryer purge valve Double D Distribution. If your semi truck air compressor isn’t building pressure, there are a few things you can check to troubleshoot the issue. theres an artillery system, an air defense system, a radar. The sound level is directly related to the amount of boost in the turbo. BTW on newer trucks governor may be integrated to air processing unit (air governor + air dryer + four vay protection valve Fist I do if compressor overbuilds air - I remove unloader line from compressor and check does it blows air if pressure goes over 125-140 PSI, if yes - stuck unloader, if not - bad governor Pablo-UA, Jul 11, 2014. My vote is that you either have an open in your discharge line, massive leak, or mechanical deficiencies with your compressor rebuild. Subject: RE: Freightliner wont build air pressure If nothing on a line, connection, or fitting comes up, drop some soapy water down along the outer face of the frame rails where the tanks mount. To lower the pressure settings, turn the adjusting screw clockwise. Disconnect the inlet and remove the governor’s line or adapter fitting. #9 Sigmars Faithful Feb 18, 2016 @ 5:40am. Truck Not Building Air Pressure One of the first signs of a problem may be that your truck isn’t building air pressure like it should. First, make sure that the air compressor is turned on and that there is power running. Takes quite a while to get up to 125. There should be no air psi on this line until at least 120 psi (depends where the air governor is set). com Trucking >HELP, building too much air!. The air pressure gauge tells you the adequacy of the air system. Once the pressure in the wet tank reaches 125-130 psi the air gov. But if they stop, pump the brakes until the pressure drops to 80 psi, and if the compressor engages and the gauges start climbing, the governor is good. I have had the unloader valve in the compressor go bad, but not very often. To lower the pressure settings, turn the adjusting screw clockwise. Wont build air pressure at idle. why Air Pressure not building up on semi truck ? (Best. Most, if not all systems, work on 120 psi of pressure. I normally fire up my wreckers every saterday afternoon to make sure everything is operating normal. Air pressure build-up from 85 psi to 100 psi should take 45 seconds or less. The secondary air pressure is dropping with the depression of the service brake pedal. 14 Answers Could be a several issues. Truck Air Compressor>3 Signs of a Bad Truck Air Compressor. If it was cold out see if the compressor head is freezing up. Once the pressure in the wet tank reaches 125-130 psi the air gov. OR will not build air pressure above a certain PSI - like 40 or 60p. Once the air pressure drops a certain point in the wet tank, the air gov. While driving, observe the air pressure gauge during build-up to ensure proper air system operation. However, the exact pressure varies between truck models and state laws. Next, check the air intake filter to see if it is clean or needs to be replaced. You wont lose air pressure overnight unless your truck is damaged. How fast should a semi truck build air pressure? 85 to 100 psi Quote From The CDL Manual: Check rate of air pressure buildup: When the engine is at operating RPM, the pressure should build from 85 to 100 psi within 45 seconds in dual air systems.