rooster 2

I posted a few weeks back about my A/C trouble. The system blows cold air for about 10 minutes, then the compressor stops working. I can tell that, by opening the hood, looking at the compressor, and seeing that the clutch is not engaging the compressor.

I replaced the temp sensor in the back of the radiator. One from an A6 with a V-6 motor interchanges just fine. I also replaced the programmer, and the dash mount climate control unit.

I also bled out some of the 134 thinking that I may have slightly over filled the system. Nope, nothing so far has solved the problem.

Someone said that there is a high pressure sensor in the evaporator, that could be causing the problem. Any advise on what exactly it is called, and how to replace it would be helpful.

Also, any other advise would be greatly appreciated. My Audi has been a hot drive this summer. Thanks!

Ur-snarf

When you bled the system did you bleed it out the low pressure (fill) side? It could be that the high pressure side is too high. See if you can find someone with a high/low gauge set to check it. The high pressure check valve is under the plastic radiator cover and should have a red cap on it. The high pressure switch is also on the same line.

hth

rooster 2

Yes, I simply bled 134 from the low port. What could cause the pressure to be too high on the high side of the system? Yes, I agree, it would be nice to get readings using a high/low guage set. I will have to ask around to see if any of my buddies has a guage set, or I guess I will be stuck taking the car to a shop for guage readings.

I just know enough about A/C systems to be dangerous. How are the high pressure check valve and high pressure switch evaluated to see if they are performing correctly? If one, or both are bad, does the system need to be evacuated in order to replace them?

Thanks for any advise!

Kneale Brownson

Who did the conversion to 134? Did they replace the orifice tube at the same time? Did they evacuate the system and replace the oil?

rooster 2

Kneale,
When I bought the car four years ago, the compressor was locked up, so I did the following work myself: I replaced compressor with one from a wrecking yard. I also replaced the receiver/dryer with a new unit, and replaced the orifice tube with the new variable type. I had the system evacuated, then I installed ester oil and 134 refrigerant. The system worked perfect for the past four years until now. Now, it cools great for about 10 minutes. Then the compressor refuses to operate, because the clutch won't activate. So, the system then only blows warm air. Any thoughts?

Kneale Brownson

Sounds like you converted properly. So things like a plugged orifice tube shouldn't be the problem.

You need access to a gauge set so you know what pressures you have. Till then, there's no knowing what you're looking for.

audiqv8

"What could cause the pressure to be too high on the high side of the system? "

A non working fan can cause the high side pressure to become too high. The fan is used to cool the freon as it enter the condenser thereby reducing the high side pressure. Does the AC unit operates on the highway? Turn on the AC and check to see if the radiator fan also comes on. If the fan doesn't come on then check the resistor pak for the radiator fan.

rooster 2

Yes, I checked last night. When the A/C is on, the fan is operating. Yea, I know, I need to check high and low side pressures to learn more.

audiqv8

You could get a set of gauges from Harbor Freight. If you converted to r134 then you should have also converted all the fittings. R12 and r134 uses different type of fittings.

Low side pressure should be about 34psi and high side pressure should be around 225psi depending on ambient temperature.

Get a set of gauges and hook them up. Start the engine and turn on the AC. See when the compressor kick off. It could also be the low side pressure switch that is causing your compressor to kick off.<ul><li><a href="http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92649">Manifold gauges</a></li></ul>