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K. Wiggins
K. Wiggins, Chevy Technician
Category: Chevy
Satisfied Customers: 2507
Experience:  ASE Certified Technician AA in automotive Technology, 15+ years in the trade
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I have a 2004 Chevy Silverado

Customer Question

I have a 2004 Chevy Silverado 1500 5.3 Ext cab, with dual zone auto air conditioning. I bought the truck used and have had problems with the A/C almost immediately. I had a bad bend door actuator I replaced, but the A/C was working only part-time. Now it quit all together. So far I know that the compressor doesn't cycle unless I jump the relay pins. I have swapped the relay out with a known good one. It does blow cold when the compressor is jumped and the low pressure side reads 50 psi. Can you help me?
Submitted: 1 year ago.
Category: Chevy
Customer: replied 1 year ago.
BTW... The low pressure side get cold and the high pressure side get very warm.
Customer: replied 1 year ago.
More info... on the relay pins 30 and 87 have power on the control side. 85 has power but 86 does not.
Expert:  Michael Moore replied 1 year ago.
This may be due to a bad cycling switch. There are 2 switches for the freon pressure on this truck. The low side switch is located on the accumulator ( the metal can looking thing at the fire wall). The switch cuts off the compressor if the low side pressure drops too low. You can disconnect the switch and use a jumper wire to by-pass the switch. If the a/c compressor engages, then the switch is bad or the pressure is too low. Since you say you have 50 psi, the compressor should come on as the low cycling switch cuts out around 28 psi. If there is no change you need to check the high pressure switch located on the high pressure line coming off the compressor. This is a 3 wire sensor, you can not by pass this switch, wiggle it around with the a/c on and see if the compressor engages. If it does then you may have a bad switch or connector. You may also want to check to see if there are any codes stored in the engine computer, the engine computer uses the high pressure switch to control the compressor, too much pressure and it turns the compressor off. If there is a code for this sensor, the a/c compressor will not engage. Also if you have a scan too that can read live engine data, you should be able to find a/c high pressure sensor data, it should read the same as the low side (not in the engine data but from a manual gauge) with the a/c off.
Customer: replied 1 year ago.
I checked the low pressure switch and it ohm'd good. there is power at the plug. I waggled the high pressure connector, but no change. I had a code reader, not scanner (poor GI), there are no codes stored.
Expert:  Michael Moore replied 1 year ago.
Since you do not have a scan tool that can read live data, you can try and check the voltage at the high pressure sensor. With the key on and the sensor unplugged, you should get 5 volts across the GRAY wire and BLACK wire. If you have 5 volts, plug it back in and check the RED/BLACK wire and see what voltage is there, should be between 4.5 and .5 volts. I do not have a chart that tells me what voltage at what psi but if there is a issue, you should have a bad reading.
Customer: replied 1 year ago.
I'll give it a shot. Is there an easy way to get to the plug?
Expert:  Michael Moore replied 1 year ago.
The best way if through the passengers wheel well, remove the wheel well liner and you should be able to get to the plug.
Customer: replied 1 year ago.
Thanks!!!
Expert:  Michael Moore replied 1 year ago.
let me know what you find
Customer: replied 1 year ago.
The harness was tight as banjo strings.... however, i couldn't get power at the plug.
Customer: replied 1 year ago.
could the harness be damaged? is there another test point behind that?
Expert:  Michael Moore replied 1 year ago.
If there is no power on the gray wire with the key on (should be only 5 volts and will not light a test light) then you need to trace the wire down. The wire goes back the engine computer. You need to make sure there are no breaks or make sure the wire is not shorted to ground.
Customer: replied 1 year ago.
The fun part.... :) I'll let you know what I find...
Expert:  Michael Moore replied 1 year ago.
.
Customer: replied 1 year ago.
You wouldn't happen to have a real wiring diagram of the system would you? the Chiltons diagram is a pos at best.
Expert:  Michael Moore replied 1 year ago.
I have the wiring diagram but no way to send it to you.
Customer: replied 1 year ago.
could you scan it and email it? otherwise I'm done till I can afford a decent manual.
Expert:  Michael Moore replied 1 year ago.
I am not able to do that, let me opt out and send this question back to the other experts, one of them may be able to help you with the diagram. Do not respond back to this post before another expert helps or the question will not be sent out.
Expert:  Juan Crespo replied 1 year ago.
Hi there. Attached, please find the requested wiring diagram for your reference. Best Regards.
Customer: replied 1 year ago.
I got it... thanks.
Expert:  Juan Crespo replied 1 year ago.
Thank you for using our site!
Expert:  Juan Crespo replied 1 year ago.
Hi again. Just checking to see if the information I provided helped you solve your issue. If it did, then kindly accept and rate my answer now. If it didn't, please reply so we can keep working.
Best Regards.
Customer: replied 1 year ago.
Nope... still trying to figure out where the fault is. Does there have to be a check engine light on to have a fault code with the a/c?
Expert:  Juan Crespo replied 1 year ago.
No. The CEL should only light up when there is an issue that increases emissions at least one and one half times the allowed parameter.Are there any blinking lights on the a/c control head?
Customer: replied 1 year ago.
Nope. The recirc light comes on at random but no flashing ligjts.
Expert:  Juan Crespo replied 1 year ago.
Going by the diagram I attached for you, can you tell me what's happening at the compressor relay; which terminals have power and which ones have ground? Also, is this a/c system automatic or manual? Do you have access to a scan tool capable of retrieving codes from the body controls?
Customer: replied 1 year ago.
Its the automatic dual zone. The relay only 86 has no power. It did work for 10 mintes today but was coming back from fishing so i didnt have my meters. I have a cheap code reader, but there are no codes. I dont have a logic probe. Just a test light, multimeter, and cheap code reader.
Expert:  Juan Crespo replied 1 year ago.
At this point I really don't know how to help you. I'll opt out and re-open the question so other experts can chime in. Please don't reply until another expert responds or the site will revert the question back to me. Best Regards.
Expert:  K. Wiggins replied 1 year ago.
Hello, just checking in to see if you still needed assistance with this.
Customer: replied 1 year ago.
Im chasing a ghost.
Expert:  K. Wiggins replied 1 year ago.
I know that feeling. With everything back like it should be what's the voltage on the dark blue wire t the low pressure switch with the connector unplugged? Also with the connector unplugged do you have continuity to ground on the black wire?
And when you were jumping 30 to 87 to get the compressor to kick on what was the outside air temperature?
Customer: replied 1 year ago.
at the low pressure switch I get 4.66 volts DC and I do have a good ground on the black side. jumping the 30 and 87 pins in the compressor does kick on.
Customer: replied 1 year ago.
Right now the outside temp is 68, projected high og 95.
Expert:  K. Wiggins replied 1 year ago.
Thanks,50 on the low side would be about right in the 90's. Was just wanting to verify if it might be a restriction causing the high side to cut out compressor operation via the high pressure switch.
I'll open this back up to other experts while I look over the diagrams a bit.
Customer: replied 1 year ago.
It's apparent that I'm getting no where in a hurry here. Refund my money . No help here.