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Doug, ASE Certified Technician
Category: Car
Satisfied Customers: 8368
Experience:  16 years automotive and OTR repair including specialized training from Toyota and Mitsubishi
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Volkswagen Jetta: I have a 2006 VW Jetta 1.9 TDI and I just

Resolved Question:

I have a 2006 VW Jetta 1.9 TDI and I just replaced my ac compressor, reciever/dryer, expansion valve, drew a vacuum on the system and refilled the refridgent. The compressor is getting 14v from the wiring harness but the high and low side of the system both stay at 85 psi I put approx. 16oz of R134a and 2oz of oil due to replacing the reciever dryer and expansion valve. The fans are not coming on which I'm guessing is due to the high pressor switch not sending a signal because there is no high pressure in the system... And the ac is blowing nice 70 degree Ir out of the vents. I have the Bentley manual also which has not helped much in this problem. Any ideas?
Submitted: 3 years ago.
Category: Car
Expert:  Doug replied 3 years ago.

You said the compressor is getting 14V.... you are saying the clutch signal is turning on and off with the AC being turned on?

Does the clutch engage or disengage when you turn the AC on and off?

Customer: replied 3 years ago.
There is no clutch it has a compressor control valve... and yes the voltage goes from 0v to 14v when the auto function is turned on and off
Expert:  Doug replied 3 years ago.
I apologize, the regulator valve.... old habits die hard.

If the regulator valve is energizing, the rest of the system is prepared to function. You said you replaced the compressor, was this for failure?
Was the compressor it was replaced with new or used?
Customer: replied 3 years ago.
The a/c functioned fine prior to hitting a raccoon which caused some cosmetic damage. It pushed the radiator housing in which broke the connector to the compressor. I was told that I could not replace the valve and connector... didn't do my due diligence enough.... and went out purchased a brand new compressor from and installed that along with the expansion valve and receiver dryer.

The compressor was not a reman or used item. Its a brand new delphi compressor
Expert:  Doug replied 3 years ago.

So the compressor is a complete unit, good.

When you went to charge the system, did you place it in a vacuum first or did you try to fill it from empty?
Customer: replied 3 years ago.
pulled a vacuum on the system down to -30 inhg for 45 mins. Then allowed it to sit for about 30 mins to ensure there are no leaks in the system.

recharged the system with a 19oz can of refrigerant

the system calls for 525g (+/- 25) or 17oz to 19oz

I put the freon in on the low side while the engine was running and I had to put the can in hot water for it to receive all of the charge since I didn't have a lower pressure on the low side of the pump.
Expert:  Doug replied 3 years ago.
Hmm... that seems a bit low; was that specification under the hood or did it come with the compressor?
Expert:  Doug replied 3 years ago.
I'm sorry you're right on spec with the 2006.

What is your static pressure after sitting for a few minutes?
Customer: replied 3 years ago.
I believe its 85psi.... or very close to that between 80 psi - 90 psi... I'll be home shortly and can tell you a definite number
Expert:  Doug replied 3 years ago.

My main concern here is that if you are getting power to activate the compressor and only seeing 85/85 pressures, either the pump isn't turning on or it is weak/wiped out and equalizing.

If your pressure is static at all times like it sounds, then that pump isn't turning. The pump is turned on via 12V to the control valve and a fixed ground..... meaning since you have 12V with the AC turned on, you either have a bad regulator valve/compressor (not too likely since it is new) or a damaged ground wire from the valve.
Customer: replied 3 years ago.
there is no other wire coming out of the compressor other than the two that are supplying power which one is the positive and the other is the negative...

I will put a continuity tester on the negative out of the supply harness and ground it to the frame again I believe I've done that before but I will check it again to make sure...
Customer: replied 3 years ago.
Another thing I am planning on testing is putting a direct lead to the ac compressor to try to jump the compressor and bypass the whole system...
Expert:  Doug replied 3 years ago.
Correct.... 12V signal coming from the AC control head and ground wire going to the front body ground. The 12V signal is turned on/off by the AC control head.... the ground never changes. If the 12V is there from the control head and the pump is not coming on, either there is a problem with the valve/pump or there is a problem with the ground wire.

Knowing that it was just in an accident that involved damage to the area, the ground wire being broken/stretched is a bit more likely here.

Do your continuity test to the ground by the driver headlight, or even just run a new temporary ground. See what happens from there.
Customer: replied 3 years ago.
well I just tried the continuenty tester on the ground out of pig tail that plugs into the compressor and I have full tone out of the tester... so the ground should be good.... I have not connected a dirrect line to the compressor like I planed, but I don't think it would do any good anyway... unless I'm missing something. I called the VW dealership earlier today and they told me that it could be the FCM (Fan Control Module), High Pressure switch or a few other things that could be an issues... any ideas?

I personally though they wouldn't be involved because when I press for the compressor to come on it has a voltage at the operating range... which should control the valve.... if the compressor control valve has a positive voltage of 14v it should either open or close... and the opposite if the voltage goes to 0v...
Expert:  Doug replied 3 years ago.
You're thinking right.... if you have voltage at the regulator valve, that is what turns it on. If it isn't turning on, there is something wrong with the valve or the compressor is bad.

I'm not sure where the dealership is going with those ideas, but consider this: if for example the pressure switch goes out of range, it shuts down the AC as a safety mechanism. You know how? By cutting the power to the regulator.

At this point I would rig your own wiring temporarily and see if you can hear the valve change when you apply voltage and ground and when you remove it (engine off so you can hear). If you can, the only other thing I could think of would be if there was a plug in the line ports of the compressor that you didn't see.... though on this one the plugs usually are large/bolt on if you get an OEM unit.
Customer: replied 3 years ago.
That is what I thought bout the sensors... it should be in a logic system which if one point fails it should shut the power off to the compressor/ valve to save the system of a under/over pressurization scenario.

Also this compressor has an internal safety switch incase there is a low freon scenario, but do you know if this switch is built into the control valve or is it another part of the compressor?

They are the large bolt on OEM type.... I'm going to try directly connect the compressor to the battery.
Expert:  Doug replied 3 years ago.

The line pressure switch is the low pressure safety; I am not aware of a low pressure switch inside the control valve. I can't say there isn't one, as I haven't had one apart, but it would surprise me if it had two low pressure safeties.
The compressor has a high pressure safety that is a valve that will discharge refrigerant over ~450 psi or so.

Do the direct connection (both 12V and ground) and listen for activation.
Customer: replied 3 years ago.
ok well I just put a direct connection to the compressor from the battery and didn't hear anything... had my wife in the car with the blower on and still nothing changed as far as the temperature went... I did conduct a continuity test from the two prongs on the compressor and it has a solid beep with 10.65 ohms as a reading but still the compressor isn't working... it seems I just have a bad compressor.... unless I'm missing something... any other test I could run to ensure this is correct?
Expert:  Doug replied 3 years ago.
Unfortunately it sounds like you may have a bad unit there. With the AC head sending the proper voltage when the AC is turned on/off, the ground intact, and you not being able to activate the solenoid for the control valve, I don't see any other reasonable explanation other than the compressor/valve being defective.
Doug, ASE Certified Technician
Category: Car
Satisfied Customers: 8368
Experience: 16 years automotive and OTR repair including specialized training from Toyota and Mitsubishi
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