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Cant get air system to pressure up..no leaks new governor.

Can't get air system to...
Can't get air system to pressure up..no leaks new governor. .I'm able to hold air pressure back with thumb at air compressor
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Answered in 1 minute by:
8/26/2014
Technician: Andy, Truck Diagnostic Technician replied 7 years ago
Andy
Andy, Truck Diagnostic Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 3,030
Experience: International and Isuzu trucks , International, Maxxforce, Cummins and Isuzu engines, Diagnostic and electrical troubleshooting specialist , Hvac and truck /trailer refrigeration troubleshooter
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Hi there ! Sorry to hear you are having trouble! My name is ***** ***** I would like to try and help if I can ! Can we start with the full vin number please ?
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Customer reply replied 7 years ago

Not by truck anymore sorry..it's a 07 mack granite my engine

Technician: Andy, Truck Diagnostic Technician replied 7 years ago
Is it a Mack engine as well ?
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Customer reply replied 7 years ago

Mp7 engine

Technician: Andy, Truck Diagnostic Technician replied 7 years ago

Do you know if it is the twin cylinder air compressor or single ?

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Customer reply replied 7 years ago

Not sure..thinking it's a single

Technician: Andy, Truck Diagnostic Technician replied 7 years ago
So with engine running , and the top discharge line off at the compressor , you are barely getting air pressure coming out? Sounds like unloader trouble in the compressor head . I would check with parts to see if there is an unloader kit available for your compressor. Unloader pistons stop the compressor from pumping when the governor sends the air signal to it saying that the tank pressure is at 120 psi .
Andy
Andy, Truck Diagnostic Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 3,030
Experience: International and Isuzu trucks , International, Maxxforce, Cummins and Isuzu engines, Diagnostic and electrical troubleshooting specialist , Hvac and truck /trailer refrigeration troubleshooter
Verified
Andy and 87 other Medium and Heavy Trucks Specialists are ready to help you
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Customer reply replied 7 years ago

How can u tell if unloader is bad have compressor of truck was going to take head apart what am I looking for..we have had mack trucks for long time first time we hade compressor problems

Technician: Andy, Truck Diagnostic Technician replied 7 years ago
It would be better if you could read the info from the label on the compressor to know which make and model you have on there but typically , the governor is mounted to the compressor and when the tank pressure reaches 120 psi , the governor sends air to the dryer to purge and also sends air inside the head to the unloader piston which is mounted in the head. This unloads the compressor and prevents it from pumping any more air until the air bleeds off the unloader piston when the tank pressure drops below 95 -100 psi , then the process starts over again.
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Customer reply replied 7 years ago

I took the 1/4" air line of the compressor going to governor have steady air flow coming from 1/4" air line is that normal or is unloader stuck I have a wabco compressor just try to get my head wrap around this

Technician: Andy, Truck Diagnostic Technician replied 7 years ago
Is the governor mounted to the compressor ? If so , there should likely be 2 lines to it ! One is for the tank pressure which is likely the one you have pulled apart. The other should only have air it once the tank pressure has reached 120 psi!
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Customer reply replied 7 years ago

Governor is mounted to firewall has 3 lines going to it one is from compressor other 2 are teed into same port on governor one goes to dryer other to tank I'm assuming. .The one coming from compressor has air flow with engine running..I plugged outgoing side of dryer with gauge Psi won't go above 20 psi same with incoming side from compressor..aired everything up with shop air everything was fine no leaks purged @120 psi

Technician: Andy, Truck Diagnostic Technician replied 7 years ago

Ok so it is rermotely mounted ! One line should be alone and goes to the tanks. The other lines that are teed together off the same port are for the dryer signal to purge and the unloader signal to the compressor to unload .

Try disconnecting the small line going to the compressor and run the engine to see if it

builds air up to 120 psi by itself.

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Andy
Andy
Andy, Truck Diagnostic Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 3,030
3,030 Satisfied Customers
Experience: International and Isuzu trucks , International, Maxxforce, Cummins and Isuzu engines, Diagnostic and electrical troubleshooting specialist , Hvac and truck /trailer refrigeration troubleshooter

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