wallyman424

Hey all, looking for some advice here. Here is a summary of the problem:

I've got an intermittent AC failure. Sometimes the AC works just fine and sometimes there is no cooling. The fan speed and servos seem to operating appropriately. I did the relay jumper test and I have both high and low speed condenser fan function, so that crosses off the ballast relay. So far every time Ive gone to investigate the problem and start the car (like just now) the AC is working great. I tested the High and Low pressure and they were fine at 250 and 15 at 2000rpm. The condenser fan is running with the relay in place. The couple times Ive had the AC failure it feels as though the compressor isnt kicking in. I dont feel or hear the initial clutch kick when I press the Max AC button. There doesn't seem to be a rhyme or reason as to when it will work or not. Today and yesterday it worked fine when I cold started the car. Earlier this week It didnt.

My issue is that I haven't been able to delve into diagnosis when I have the failure present. What is the most likely culprit? 3 level pressure switch? Evap temp sensor?

I guess I just have to keep trying and hope I catch the fault in action.

95_993

What is the ambient temp when you're measuring the pressures? It's a very low volume system so being on the low side of the range 15-17psi low pressure side, you may be just a little low on freon. What is the temp of the air coming out of the vents when it's working?

wallyman424

Ambient air temp is around 90F. When its working it blows cold (don't have an exact temp for you). But when its not working its completely not working. I don't think its a problem with the system charge, I'm leaning more towards and intermittent electrical fault from one of the sensors that controls the compressor on/off.

ToreB

Leaks are the most common cause for no A/C compressor activation. A pressure switch will turn off the compressor activation signal if the pressure is too low or high.
You can use a Porsche compatible OBD tool to read out any fault codes in the Climate Control Unit. This will tell you if there's a (unlikely) problem with a sensor.
Be sure to set the temperature control to minimum and fan to 1 or above when testing, and you can use either A/C button.
DIY test of all servos and fans here: https://www.bergvillfx.com/porschehvac1
Cheers,
Tore

AZ993

Bummer about the AC. Just to throw this out there... I had an intermittent issue with the “max” AC button not working. Symptoms, regular AC button would work. The max AC button didn’t consistently override and cause max fan speed, closure of upper/lower vents.

A thread on Rennlist suggested disassembly of the faceplate of the CCU and contact switch cleaning. I used Tore’s website as a guide for disassembly. For me it worked. Thread below:

https://rennlist.com/forums/993-foru...x-problem.html

I wonder if it could be similar issue if it’s only intermittent.

PRSWILL

So I had an intermittent issue this spring. I found that the ground wire to the compressor was loose- there's a blade-style connector inside of a little clear case just inside the plastic cover by the oil fill. The blade has worked it's way out of the butt-end and was barely touching if at all and the compressor would kick off and on... I think it got knocked loose during an oil change. Anyway, Plugged it back in and COLD air again! YAY! Check it out... may be that simple for you as well OP.

wallyman424

What year is yours? Mine's a 95 and the compressor clutch grounds to the compressor mount. I think its different after the addition of varioram.

badabing

Hijacking this thread since I have some AC minded people here, quick question:

When I evacuated the system I failed to observe how much oil was removed. How much typically needs to be injected when using a professional machine to evacuate?

System capacity is around 3.5 Oz

Cactus

Mine stopped cooling so I grabbed a can of A/C Pro from Autozone. Filled until the gauge was in the green and there was cold air. It was a hail Mary because I was going on a long road trip the following weekend and it was in the 90's. That was mid June and it is still working.

PRSWILL

Mine is a 96 C4S. The ground comes off the compressor and to the frame right by the oil fill.

wallyman424

Update on this problem.

The problem became persistent which was bad, but also good because it made diagnosing it a lot easier.

Turns out it was the R01 relay (rear fog light/backup light) that was failing not sending power to the AC compressor relay. I stole my sunroof relay for the time being until the new one arrives.

Good to have AC now that summer is coming in FL

SpeedyC2

I had the very same issue, and the same easy fix on my '95 not long after I got the car.