94 XJS. New compressor, evaporator, charged system. a/c blows cold for 20 minutes, then warm air. Turn key off & wait 10 minutes, a/c blows cold air. A/c shop cant find any leaks. Any ideas people?

 

If you pull out ("click") the left hand temperature knob, this should set the aircon to full cold and over-ride the system. Does it stay cold when you do this?

Greg

 

Don't think you can pull out the temp knob on a 94MY, at least not on a car that was made after about December 93.

There is a manual control button on the top right of the panel however.

Your problem may be electrical. Have you tried listening to the compressor to ensure it is clicking on and off? Hit the Aircon button on and off and listen.

You may have a bad connection to the compressor, check that the voltage to the compressor is steady.

Next, perhaps check the motorized aspirator and the evaporator temp sensor. If they did not reconnect or reposition the evaporator sensor correctly that could be an issue.

Another possibility is the heater valve, if it is stuck open then the cold air would have to pass through a now hot heater core resulting in lukewarm air.

Another issue could be a partially blocked condenser or defective receiver/drier. You don't mention that they were replaced with the other bits?

 

Or expansion valve.

Or the system incorrectly charged.

Ask the repair shop specifically if the pressures are staying in range. They've probably already checked....normal procedure....but try to pin them down a bit and make sure.

If the refrigeration aspect of the system is removed as a possible culprit you can then look at the control side of the system.

Cheers
DD