A/C Compressor Troubleshooting

[sahls01gmc]

Thanks for the thorough response! I tried to be as descriptive as possible, and I believe I have it all worked out now. With the compressor acting as normal as I would have hoped for, I am going to re-install it for now. New ones run about $250, and I already know how to get it in and out now. I have the new gaskets already along with a new tensioner and belt, so should be about good to go. I'll replace the drier as I re-install everything, and try to charge it and see what happens.

 

I'll have my shop (I work for Cummins) do all of the re-charge work, and hopefully we will have cold air once again!

 

Thanks again!

[Doug_Scott]

don't install receiver/drier until you are ready to vacuum and service it. Maybe even pay your shop to install new one after you get there. Being open for a few minutes won't hurt, but, driving for a half hour on a humid day may kill the desiccant.

[sahls01gmc]

Noted. Perhaps I will mock up the new drier, but leave it sealed up until I am ready to charge. Then I will hook it all up on site.

 

Thanks for the tip!

 

 

For the record, I fully realize this type of a job usually would be better off in the hands of the "mechanic". But I also am a guy who goes by the motto "Give a man a fish, he eats for a day.........", and I love the opportunity to learn something new. Sure, I may spend about the same money replacing a few extra parts and investing a lot more time, but the new knowledge is priceless to me. That is why I try to come on this forum and find out exactly what I need to so that I know when something is over my head or not. I have a garage full of tools, and the drive to want to fix my own things.

 

 

Thanks to all of you for your assistance!!!

[grampadirt]

Man you sound just like me,I too like to learn something new and not afraid to make mistakes.Good Luck on your A/C

 

 

BTW,I see your truck has 245,000m....same as my burb

[sahls01gmc]

Here's the update as of last night. I installed the new tensioner, belt and gasket that go on the lines that connect into the compressor. I re-installed the original compressor as I wasn't seeing anything that led me to believe that it wouldn't work. When I turned the truck on, I could see that the compressor pulley was spinning just fine, no squeaks or anything. When I turned on the A/C, I didn't happen to notice a difference under the hood (I know I will not have cold air until it is re-charged). Should the front plate start spinning once the command for A/C is made? Usually, I can tell when the compressor kicks on because you know the load is being put on the system. What diagnosing can/should I do in regards to checking normal function of the compressor? Like I said previously, it all seemed normal and ok on the bench, so I'm not sure if I should expect anything on the truck.

 

New drier and orifice tube are on the list for this weekend, and possibly the compressor if I can determine if it is good or not.

 

Any more thoughts or ideas are certainly encouraged!

 

Thanks

[txab]

Compressor will not run until you get refrigerant in it. There is a pressure switch that controls the compressor operation. Did you lose any oil from the compressor while you had it off?

[Doug_Scott]

Compressor requires refrigerant to be in the system before it will engage. Since the oil is carried by the refrigerant, running the compressor without it will kill compressor pretty quick.

Once system is charged, compressor should engage and run for a bit, then cycle off and on depending upon pressures on the low side. If it is cycling quickly, generally means it needs more refrigerant, but, you should be using a proper gauge set to fill the system. Most car a/c systems specify refrigerant capacity in pounds(weight).

[sahls01gmc]

I did not lose any oil that I know of. I know I never turned it upside down, am I correct in assuming the oil would come out of the connections for the hoses? I also covered up the hose connections on both sides to minimize what "could" get into the system. Makes sense on the pressure switch....is that what keeps the compressor from engaging because it would assume there is no oil? Right now it is only spinning on the pulley, so I believe I'm safe.

 

Thanks for the tips, it all makes sense when I compare what I "hear" to what I "see".

[Doug_Scott]

Effectively, yes, it does this to prevent the compressor from running without proper lubrication. As said earlier, the refrigerant carries the oil around, much like a 2 stroke fuel system.

[gmtech4]

FYI

 

A/C Operation

The purpose of the air conditioning (A/C) system is to provide cool air and
remove humidity from the interior of the vehicle. The vehicle operator can
activate the A/C system by placing the mode switch in one of the following
positions: Panel, Bi-Level, Defog, and Defrost. The A/C system can operate
regardless of the temperature setting, however, recirculation is only available
when the HVAC control module is either in A/C or Bi-Level mode only.

When the A/C button is pressed a request is made to the powertrain control
module (PCM) to turn on the A/C compressor. The PCM turns on the A/C compressor
by providing a path to ground through the A/C clutch relay control circuit for
the A/C compressor clutch relay. Once the relay closes its internal switch,
power from the battery is provided to the A/C compressor clutch through the A/C
compressor clutch supply voltage circuit. Whenever the compressor is turned off,
the A/C compressor clutch diode provides a path for the voltage spike resulting
from the collapsing magnetic field of the compressor clutch coil.

In order for the PCM to internally ground the A/C clutch relay control
circuit, the A/C low pressure switch signal circuit needs to be grounded and the
A/C request signal circuit needs to have 12 volts applied to it from the HVAC
control module. A 12-volt reference signal is sent out over the A/C request
signal circuits from the HVAC control module, through the A/C high pressure
switch and then to the PCM when the vehicle operator makes an A/C request. A
separate 12-volt reference signal is sent out over the A/C low pressure switch
signal circuit, through the A/C low pressure switch and the ground circuit.

The PCM will engage the A/C clutch any time the engine speed is below
5000 RPM and the A/C is requested unless any of the following conditions exist:

• Throttle angle is at 100 percent.
• 
  
• The A/C low pressure switch is less than 124 kPa (18 psi) or more than
  338 kPa (49 psi).
• 
  
• The A/C high pressure switch pressure is more than 2896 kPa (420 psi).
• 
  
• Engine speed is more than 5500 RPM.
• 
  
• Engine coolant temperature (ECT) is more than 121°C (250°F).

A/C Pressure Sensors

The A/C system is protected by two pressure switches. The A/C high pressure
switch interrupts the A/C request signal when the A/C line pressure exceeds
2896 kPa (420 psi). The A/C low pressure switch interrupts the A/C low pressure
switch signal when the A/C line pressure falls below 145–172 kPa (21–25 psi).
When the PCM sees an open in either signal, the A/C clutch relay control circuit
is no longer grounded, thus shutting off the compressor. The low pressure switch
will close when pressure reaches 262–290 kPa (38–42 psi).

 

Recirculation Mode

The recirculation door will move automatically with an input from the A/C
high pressure recirculation switch at approximately 2413 kPa (350 psi). The PCM
will place the A/C system in recirculation mode when a signal is sent over the
A/C refrigerant high pressure cut-out switch signal circuit. The recirculation
actuator door control circuit is grounded by the PCM to ensure that the actuator
is forced to the recirculation position. This allows for the cooler inside air
to flow over the A/C evaporator and cool the refrigerant, until the high side
pressure returns to normal. This action will allow the high side pressure to
return to normal pressure at a faster pace. The recirculation door will move
back to the outside air position when the high side pressure reaches 1724 kPa
(250 

[sahls01gmc]

Wow, awesome info! Thank you!

[gmtech4]

welcome

[sahls01gmc]

Alright, here is the latest update. I have replaced the accumulator and orifice tube, and was able to get almost 1lb of R-134 into the system which put it at about 50psi. When I turn on the A/C, the compressor still does not engage.

 

What other things should I look for? Where doe sthe compressor get the signal to turnon from?

 

Could the temperature control dial on the dash have anything to do with this?

 

Let me know if you need more information.

 

 

 

Thanks!

[Doug_Scott]

You should be filling the system with the vehicle running, a/c set to cold (or if auto a/c set to a temp well below current temp), and does not need to be on recirculate. As said before, my experience is with R-12, not R-134a, so not sure how current setups sit, but, R-12 systems would have a pressure equal to the ambient air temp when a/c was not turned on. You would see this pressure if there was one pound in the system, or 5 pounds in the system. High side pressure on R-12 would be double ambient air temp when a/c is running.

 

All that just so I can say that you need to fill from low side, and fill with engine running, a/c turned on. You should also have a gauge on the high side as well. You did not mention running a vacuum on the system before filling. You should have run a vacuum on the system for about 30 minutes before filling the system.

 

Low side pressure switch will be located after the fixed orifice tube, and before the compressor on the low side line. Back in the day, GM mounted the switch either on the receiver/dryer, or on the line in or out of the receiver dryer. It was always before evaporator as well. You can force it to work by unplugging the switch, and connecting the two wires together in the plug you just pulled off. Short jumper wire, or cotter pin will suffice, but, do not leave it in, just connect for short periods of time. Once there is enough in the system, the switch should start working.

[gmtech4]

Alright, here is the latest update. I have replaced the accumulator and orifice tube, and was able to get almost 1lb of R-134 into the system which put it at about 50psi. When I turn on the A/C, the compressor still does not engage.

 

What other things should I look for? Where doe sthe compressor get the signal to turnon from?

 

Could the temperature control dial on the dash have anything to do with this?

 

Let me know if you need more information.

 

 

 

Thanks!

please refer to post #25

 

then take it to a shop