Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Hi, I'm Chad. Welcome to JustAnswer. I'm reviewing your question and I will be posting your reply ASAP.
are you saying you jumped the pressuer switch by jumping the connector for it and ac clutch came on ?
or the ground was missing ,you added ground it came on? where did you add ground to at what point in the circuit ?
please let me know
Thank You *****ASE Certified Technician
if that is the case , and you already changed ecm
You need to do a continuity test on the ground wire coming from ecm to relay and see where it is broke .
follow the color wire all the way back to ecm.if the giving ground is making it run at relay ,then from relay back to ecm must be the issue
do you have auto or manual ac controls ?
ok will it is manual control then
question the blower motor is still working on inside the cabin ?
if the blower is working and you are missing the ground the ground comes from the pcm based the wiring diagram for your truck
The dark Green & White wire is the wire coming from the pcm to the Relay as you can see in the diagram provided
Please let me know if you need anything else on it, just reply back & we will continue
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Thanks You Chad FarhatASE Certified Technician
how about ground
yes , it needs to cycle ,if it stays on 4 hours the lines will freeze and no more cooling.
what you can do, id drive ,run it and every 10 minutes cut it off 2 minutes .
the compressor will lock up on you if it stayed on 4 hours, so you do the cycling yourself by switching it on & off
The ECM does provide ground to the relay .
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you mean you test it out ecm pins and you had high resistance on some pins or all , is this what you mean.?
what is the reading on PIN 85 on the compressor relay ,switch on ?
do you have a ground on that pin ,it should be the one coming from PCM, dont worry about what color it is , are we getting a ground on that pin to complete the circuit and activate that relay ?
ok what is on pin #1, the one to ecm ,is there ground on it ,with igntion switch on, a/c on switch also ,?
does pin# ***** wire, does it pass a continuity test between relay & ecm ?
if your wire is good , then that leaves ecm is not sending ground to the relay.
what is the mileage on the truck, any after market radio or stereo tied it to same circuits ?
all frame to engine block grounds checked ?
I m sorry man ,i m not sure which way to go on this one, So i will open up your question & opt out for another expert to help you on it.
Hi there. Different expert here - previous expert opted out.
In addition to an A/C request from the A/C control head, the PCM needs to see "good" signals from throttle position and engine temperature sensors before it will switch the circuit to ground the relay. Is there any indication of a problem with either one of those three signals? Check Engine Light on? Engine misfiring or overheating?
Can your reader report on A/C request status or just retrieve codes?
Well, according to the Innova website, the 3040C can read live data; they just don't say which specific parameter data indicators. Let's hope it does read A/C request - the parameter might be displayed as a simple YES or NO. Please let me know what you find out.
OK. I need those 3 code numbers as they might be what's preventing the PCM from supplying ground to the A/C relay.
Also, you'll need to set the reader to display live sensor data, then look for A/C request; is it ON or OFF?
I'm not familiar with your reader. I'm just going by the Innova website claims the 3040C can do.
In any case, can I at least get the code numbers so we can be sure that's the root cause of the issue?
OK, then we're left with testing for power and ground at the PCM as our only recourse - problem with that is that we won't know if the PCM is or not processing the signal.
Would you like me to upload the circuit diagram for you to check those powers and grounds?
Let's hope is not a defective one. I'll be off starting tomorrow evening and won't be back for at least two weeks - could be longer.
Use the attached diagram for reference - RED means system voltage, GREEN means ground. Perform all checks with engine running at idle and A/C turned ON, blower on HIGH.