1992 Sierra K2500 5.7L 4x4 Air conditioning L

[Disloc8r]

Today i replaced my a/c compressor and dryer hoping to fix my air conditioning problem. After the work was complete the compressor would not cycle so i could charge the system. Fuse in the panel is fine. I checked the wires going to the valve on the dryer and was not getting any voltage. Tried tracing wires but got lost in the main harness in the firewall. I am assuming that there is either a wire problem or a relay problem. Does anyone know where the relay is if there is one? The pickup has never been modified and has just over 90k miles.

Thanks all

 

[Molson02536]

Today i replaced my a/c compressor and dryer hoping to fix my air conditioning problem. After the work was complete the compressor would not cycle so i could charge the system. Fuse in the panel is fine. I checked the wires going to the valve on the dryer and was not getting any voltage. Tried tracing wires but got lost in the main harness in the firewall. I am assuming that there is either a wire problem or a relay problem. Does anyone know where the relay is if there is one? The pickup has never been modified and has just over 90k miles.

Thanks all

Did you vacuum out the A/C system first before you tried to recharge it?? Once you have vacuumed out the system to ensure you have no moisture, you start to recharge it with a recharge machine with gauges to read your high and low side readings.

High pressure gauge: When the reading gets up around 200 to 225 psi (R12), or225 to 250 psi (R134a), STOP. The system is fully charged and should be cooling normally. DO NOT add any more refrigerant.

LOW pressure gauge: When the reading is between 25 and 40 psi with the A/C running, STOP. The system is fully charged and should be cooling normally. DO NOT add any more refrigerant. If the gauge is over 50 psi, you have overcharged the system with too much refrigerant.

NOTE: The high and low pressure readings will vary depending on the system and ambient temperatures (higher temperatures cause higher system pressure readings).

Refer to the vehicle manufacturer specifications for normal system operating pressures, and the total refrigerant capacity of the system. Most newer passenger car A/C systems do not hold much refrigerant (only 14 to 28 oz.), so you don't want to add too much if the system is low. One can of R134a typically holds 12 oz. of refrigerant.

NOTE: The compressor may not engage if the system is too low on refrigerant. The low pressure cutout switch will prevent the compressor from running if the system is too low on refrigerant (this is done to protect the compressor from damage due to a lack of proper lubrication). The compressor must be running to suck refrigerant through the service hose into the system. So if it is not engaging when you turn the A/C on, you may have to supply battery voltage directly to the compressor clutch using a fused jumper wire. Look for a single wire connector near the front of the compressor, unplug it and hook up a jumper wire to the battery POSITIVE terminal. This should cause the clutch to engage and the compressor to run.

 

[Disloc8r]

Ok we did the jumper to the posts from the battery. With this we were able to get a full charge in the system and cold air while the system was bridged. After we connected it with the stock plug the comp clutch would not engage on its own. Again back to where I started. My truck does not have an under the hood fuse block or relay panel just the one on the firewall where the fuel pump relay is. We checked all relays behind the glove boxand two were fan speed relays and I don't remember what the third was. The only relay on the panel under the steering column was flashers and something else. There has to be a compressor clutch relay somewhere the question is where. It could also be a wire that has gone bad somewhere. All components are working properly including low pressure shut off switch. Any other ideas?

 

[Molson02536]

Ok we did the jumper to the posts from the battery. With this we were able to get a full charge in the system and cold air while the system was bridged. After we connected it with the stock plug the comp clutch would not engage on its own. Again back to where I started. My truck does not have an under the hood fuse block or relay panel just the one on the firewall where the fuel pump relay is. We checked all relays behind the glove boxand two were fan speed relays and I don't remember what the third was. The only relay on the panel under the steering column was flashers and something else. There has to be a compressor clutch relay somewhere the question is where. It could also be a wire that has gone bad somewhere. All components are working properly including low pressure shut off switch. Any other ideas?

The A/C relay is Under Instrument panel on top of heater-A/C case.

First, Check the A/C heater 25 amp fuse. Then Check the light green wire going to the low side pressure switch. The low pressure switch is normally mounted to the acculmator.

If you are getting power on the light green wire at the pressure switch with the engine running and the a/c is turned on, the relay is working. Then try jumping the light green wire to the dark green wire at the pressure switch to see if you then get power to the compressor.

If no power to the light green wire, we need to see if the AC controller is suppling a ground to the relay. The ac controller grounds the relay on the Dark blue wire with the white stripe.
Check these and let me know.

http://ww2.justanswer.com/uploads/GMGreatWrench/2009-09-19_031651_92_blower_ac_relay.gif

 

[Disloc8r]

Ok, we checked the fuse and it was ok. We checked the light green wire and there is no power going to the low pressure switch. There is also no power going to the compresser. We took the whole dash apart and could not find the relay other than the one behind the glove box that had the dark blue/white stripe and it is not grounding the ac controller. We were unable to find the ac controller. Do you know where it is located and what it looks like? Ultimately there is no power going to the pressure switch of compressor so it has to be a relay or controller problem at this point. The relay that was labeled number 3 in the diagram is working properly and i switched out a new one just to make certain. i checked all 3 of the relays by switching out with new ones just to make sure they were all good.

 

[Molson02536]

Ok, we checked the fuse and it was ok. We checked the light green wire and there is no power going to the low pressure switch. There is also no power going to the compresser. We took the whole dash apart and could not find the relay other than the one behind the glove box that had the dark blue/white stripe and it is not grounding the ac controller. We were unable to find the ac controller. Do you know where it is located and what it looks like? Ultimately there is no power going to the pressure switch of compressor so it has to be a relay or controller problem at this point. The relay that was labeled number 3 in the diagram is working properly and i switched out a new one just to make certain. i checked all 3 of the relays by switching out with new ones just to make sure they were all good.

Here is another link to show you where all the relays are. #12 is RELAY,A/C CMPR(1 BOLT HOLE, 5 TERM, SKIRTED)(4.720)(ACDelco #12088594) and #5 is the MODULE,AUX HTR & A/C CONT(8.852)(ACDelco #15-73379)

Good luck and keep me posted.

http://www.compnine.com/index.php?u...modelseries=NULL&uid=1&modelid=6922&capuid=1&