2003 Silverado A/C Help

[75sierraclassic]

I just bought a 2003 Silverado LS with 160,000 miles. The A/C has been giving me fits. Sometimes the compressor will turn on sometimes it won't. The A/C button in the cab is sticky but the light on the button comes on every time I push the button to turn on and turns off when I turn it off. It seems to turn on when the truck is cool but if you shut the truck off and turn it back on when its hot (with the A/C button still on) the compressor won't kick on. I put some hoses on it and took pressure readings but I'm not sure what they should be. See below. Ambient temperature was in the low 90's. I ran it for about 10 minutes and the compressor never cycled.


Engine RPM: Idle 600
Low side PSIg: 62
High side PSIg: 320
Cooled Interior Air Temp F:66

Engine RPM: 1500
Low side PSIg: 290
High side PSIg: 45
Cooled Interior Air Temp F:56

Engine RPM: 2000
Low side PSIg: 45
High side PSIg: 280
Cooled Interior Air Temp F:58

I tried to jump the low side pressure switch when the compressor wouldn't turn on and it still didn't turn on. I havent tried to jump the high side switch.

Any thoughts on what it could be?

[Sillyoldman]

bump

[clinebarger]

Originally Posted by 75sierraclassic

I just bought a 2003 Silverado LS with 160,000 miles. The A/C has been giving me fits. Sometimes the compressor will turn on sometimes it won't. The A/C button in the cab is sticky but the light on the button comes on every time I push the button to turn on and turns off when I turn it off. It seems to turn on when the truck is cool but if you shut the truck off and turn it back on when its hot (with the A/C button still on) the compressor won't kick on. I put some hoses on it and took pressure readings but I'm not sure what they should be. See below. Ambient temperature was in the low 90's. I ran it for about 10 minutes and the compressor never cycled.


Engine RPM: Idle 600
Low side PSIg: 62
High side PSIg: 320
Cooled Interior Air Temp F:66

Engine RPM: 1500
Low side PSIg: 290
High side PSIg: 45
Cooled Interior Air Temp F:56

Engine RPM: 2000
Low side PSIg: 45
High side PSIg: 280
Cooled Interior Air Temp F:58

I tried to jump the low side pressure switch when the compressor wouldn't turn on and it still didn't turn on. I havent tried to jump the high side switch.

Any thoughts on what it could be?

Do you have a Manual A/C or Auto A/C control head?

Those pressures are high. 320 PSI of head pressure is hard on the compressor. Check clutch fan operation, Check for a clogged condenser, A/C system maybe over charged..Spec is 1.6 lbs of 134A, clogged orifice tube, To much refrigerant oil..Spec is 7.1 oz.

[75sierraclassic]

I'm not sure what you mean by manual or auto A/C controls. It has the dual temperature climate control unit.

Should I jump the high side switch to see if it is what's stopping the compressor?

I need to run a lead to the compressor to see if its getting voltage when it shuts off.

Any other things to check without having to discharge the system? Could it be the switch in the control panel?

[clinebarger]

Heres a pic of my 04, It has auto A/C. A manual control head will have 2 slides on it. Do not jump the High side pressure sensor...It wont do any good, its a Sensor not a on/off switch. The easy way is have it "scanned" with a GM Tech 2 scan tool to see if the PCM is receiving a A/C request from the control head, If it is the control head is good. The PCM has control over the Compressor clutch & It will cut power to the compressor clutch under the following conditions:

The A/C high side line pressure is over 429 psi.
Throttle angle is at 100 percent.
Engine speed is more than 5500 RPM.
Engine coolant temperature (ECT) is more than 250°F.
Ambient air temperature is less than 40°F.
(Even with a "A/C request" from the control head)

There are ways to check "some" of this stuff without a scanner, But I need to know what Control Head you have.

[75sierraclassic]

I have the manual control with 2 slides.

[clinebarger]

Next time it happens jump the A/C comp. relay Pin 87 to Pin 30, The pins are labeled on the bottom of the relay to help you know what pins to jump in the fuse box. The compressor clutch should kick in, Jump it momentarily, your just checking the curcuit & clutch!

If the clutch does engage, stop & install your gauges, Jump it again....If high side pressure exceeds 350 psi STOP (pull the jumper), You have a airflow problem, stopped-up, over charged or over oiled system.

[BP68]

I agree about checking the condensor. I have seen these get packed with dirt/leaves/etc between the condenser and radiator.

[75sierraclassic]

Thanks for the help guys, it has been coool enough for the past week that it hasn't shut off. I'm hoping for hot weather so I can get it figured out.

[truckdude239]

sounds like your fans aren't working right driving up the pressures, no air flow over the condsor will cause high pressures

[75sierraclassic]

I just drove home from work and it was 85 F outside. A/C quit working and tried to get the relay out, damn thing is in there good. Gave up as I have to be somewhere. I did check the fan though and while it was hot just after I turned it off, i could turn the fan freely. Does that mean my clutch is shot? If the clutch is shot and thats causing my A/C to shut down, wouldn't the engine be overheating too?

[clinebarger]

Originally Posted by 75sierraclassic

I just drove home from work and it was 85 F outside. A/C quit working and tried to get the relay out, damn thing is in there good. Gave up as I have to be somewhere. I did check the fan though and while it was hot just after I turned it off, i could turn the fan freely. Does that mean my clutch is shot? If the clutch is shot and thats causing my A/C to shut down, wouldn't the engine be overheating too?

Sounds like a bad fan clutch, It wouldnt necessarily make the engine overheat.

[75sierraclassic]

Well nothing helped. I put a new fan clutch on and that didn't help. I also tried to jumper the relay from pin 87 to pin 30 when the compressor quit working and nothing happened. The compressor still didn't kick on when I jumped it. The condenser is not plugged with any leaves or other debri. So does that just leave me with it being the body module or the HVAC controls in the dash?

[clinebarger]

Originally Posted by 75sierraclassic

Well nothing helped. I put a new fan clutch on and that didn't help. I also tried to jumper the relay from pin 87 to pin 30 when the compressor quit working and nothing happened. The compressor still didn't kick on when I jumped it. The condenser is not plugged with any leaves or other debri. So does that just leave me with it being the body module or the HVAC controls in the dash?

Jumping the relay pins gives "Direct" control of the compressor clutch....If your jumping the correct pins...Check for 12 vdc at the dark green wire on the compressor clutch plug, If thats good check the ground(black wire).

If you have good power & ground to the clutch, Suspect a bad(going bad) clutch coil or excessive clearance between the clutch plate & hub.

Heres a diagram...

[75sierraclassic]

Thanks for the input, I apparently beat you to it. I ran a lead to the coil connector and monitored voltage. It has voltage and the compressor isn't turning on. FUDGE!!!!!!!!. Trying to find a new compressor now. Should I defenitely get a GM one or go for the auto parts store?

[75sierraclassic]

Well rather than replace the entire compressor, I'm just going to try and put a new clutch on. Bought this last night and hope it goes on fast tonight.

http://shop.advanceautoparts.com/web...ral#fragment-2