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Gary
Gary, ASE Certified Technician
Category: Chevy
Satisfied Customers: 742
Experience:  Senior Technician
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We have a 2007 3500 with the 6.0 that the A/C does not work.

Customer Question

We have a 2007 3500 with the 6.0 that the A/C does not work. New compressor, high and low side switches, orifice tube and dryer. System works if you jump the comprssor relay. We need some sort of diagrams or steps to take.
Submitted: 1 year ago.
Category: Chevy
Expert:  Gary replied 1 year ago.

I am sorry your having this problem

any access to a scan tool to see live computer data ?

the 3 wire a/c pressure switch was changed ?

do you have a test light or multi meter on hand ?

Customer: replied 1 year ago.
the 3 wire switch was changed and I have a multimeter.
Expert:  Gary replied 1 year ago.

here is the charts we need to follow next

the engine temp in the dash is reading correctly ?

with the key ON and you unplug the 3 terminal connector does the grey wire terminal in the connector show 5 volts ? is the tan a good ground ?

Expert:  Gary replied 1 year ago.

here is the wiring for that circuit

Customer: replied 1 year ago.
The colors of the harness at the 3 wire switch were red which had about .5 volt and same with the black wire the tan wire was a soild ground
Expert:  Gary replied 1 year ago.

are you able to see what the pressure switch is reading in the live computer data with it plugged in ?

Customer: replied 1 year ago.
Nope we are not able to do that
Expert:  Gary replied 1 year ago.

what bothers me is you show 5 volts but the other 2 wires are showing ground

only one of them should be

the tan is the ground and the other NON 5 volts wire is the signal wire to the ECM for the pressure signal

and if that wire is shorted to ground or the computer is bad causing that ground the AC will not work getting a false signal from that wire and not allow the ac to run

Customer: replied 1 year ago.
I said .5 they have a 1/2 volt
Expert:  Gary replied 1 year ago.

my mistake

at this point with everything you have done we have to try to follow that chart but we will keep running into issues to follow the chart with not being able to read live data and perform the tests with the scan tool to find this problem out

at this point this should boil down to a bad reading the computer is seeing to not allow the ac to turn on of the controller is not telling the computer to turn on the ac

Customer: replied 1 year ago.
The relay for the compressor just caught fire while i was re testing the three wire plug
Expert:  Gary replied 1 year ago.

are the terminals the relay plugs into melted ?

Customer: replied 1 year ago.
No they are fine I saw it before things melted.
Expert:  Gary replied 1 year ago.

replace the relay and be sure the terminals the relay plugs into are making good connection to the relay terminals and will the ac still not work ?

Customer: replied 1 year ago.
Still nothing
Expert:  Gary replied 1 year ago.

lets see if another expert has any ideas

hang on another expert will reply back to you

Expert:  Gary replied 1 year ago.

Hi there,

Are you measuring the 3 wires at the sensor while connected or disconnected?

If you are disconnected, you need to find out why you only have .5 (1/2 Volt) instead of 5 Volts.

That is where I would be going with your problem.

Gary (HoldenTech)

Customer: replied 1 year ago.
Okay
Customer: replied 1 year ago.
This all i can see with my scanner
Expert:  Gary replied 1 year ago.

Going from the circuit above, and all A/C pressure sensor circuits in general, you need to have 5 volts, ground, and sensor signal.

Depending on the scan tool, it may say normal, but your ECM may interpret the signal as low if the 5v or signal wire is bad, or high if the ground is bad. Either way when the signal wire voltage is outside of programmed parameters the ECM does not allow A/C clutch engagement. The purpose is to protect the A/C system if pressure is truly high or low.

I've had an o/c ground on a car that didn't allow the system to work.

I've also had a partially shorted 5v supply which was only 3v which had no A/C.

Can you measure the 5v wire with the sensor disconnected again?

Have you verified the ground wire is truly ground, zero ohms?

Have you checked the sensor wire end to end for continuity, and no short to ground or voltage?

Gary

Gary

Customer: replied 1 year ago.
Okay i have three wires a red one with 3 volts a grey with 3.5 and a black one that has a couple mil ohms like 3 to 4
Customer: replied 1 year ago.
The wiring diagram i was sent is impossible to read as far as wire numbers etc its to low res
Expert:  Gary replied 1 year ago.

Ok, sounds like you have a bad ground which is supplied from the ECM.

This circuit would be similar in operation to yours:

The Black wire should read zero ohms to ground while the ECM is still connected.

Gary

Customer: replied 1 year ago.
Where would the grounds for the pcm live?
Expert:  Gary replied 1 year ago.

Your pressure sensor ground is supplied from the PCM.

If the engine runs fine, then this supplied ground could still be internal fault of the PCM.

You are measuring the black wire to ground while the PCM is connected and the sensor is disconnected?

Should be Zero ohms.

Gary

Customer: replied 1 year ago.
Well that wire has 3.5 volts on it at the moment. .. disconnected from the sensor
Expert:  Gary replied 1 year ago.

If we back track for a moment, you said your red wire has 3 volts, your grey has 3.5, and now the black also has 3.5 volts?

Is that all measured at the pressure sensor connector while it is disconnected from the sensor?

Gary

Customer: replied 1 year ago.
My bad the black still has some resistance on it .... what would cause the low voltage on the red wire and why would the grey wire (assuming it is running to the pcm) have power on it at all if the connector is unplugged.
Expert:  Gary replied 1 year ago.

Ok, with the sensor disconnected, you should see 5 volt on the red wire, no volts on the grey wire, and ZERO ohms (measuring resistance not voltage) on the black wire.

To me, you are seeing near the same voltage on the red and grey.

If that is the case, the red and grey could be shorted in the harness.

Can you verify that there is no short from red to grey with the sensor and PCM disconnected?

Gary

Customer: replied 1 year ago.
What is the path for these wires in the harness is there a readable diagram?
Expert:  Gary replied 1 year ago.

Hi again,

I don't have access and can't find a harness routing diagram.

The best I can suggest is the sensor harness wires would run from the sensor directly within the engine harness to the PCM.

I'd say you have a broken wire within the harness.

What was your voltage, continuity test results of the 3 wires?

Gary