I pulled in to the grocery store today with a/c blowing so cold that I had just turned it down on low. I parked, turned the a/c off, then turned the car off and went inside. When I returned and started the car the a/c is blowing hotter than the air outside. 100 degrees in San Antonio. Car is 1998 xj8 vdp. Does anybody have a clue?

 

Check to make sure your a/c is set to recirculate. Check Freon levels, then check electrical, like fuses, switches, relays.

 

As old as your car is (I have a 98’ also), besides what Randy mentioned, checking the A/C compressor relay (and all the other brown relays throughout the car because of age) would be a great place to start. Inside the relays where the contact points are is where they burn up at. If it’s not terribly burned up, they can be cleaned up with a small flathead screwdriver or a file. The most common brown relays that fail in these cars is: starter, A/C compressor clutch and fuel pump. These are the higher load items that make them wear out quicker than the rest. Now, I’m not saying that your compressor relay is bad but, I would start there because you said it was blowing cold a short time before it started blowing hot. Unless an A/C hose decided to blow while you were in the store, it’s possible because of the engine heat soak could’ve made the old rubber hose blow.

 

When my xjr ac started to blow hot air after hot start and after few km s of driving started to blow cold air. It was eventually broken ac pressure sensor that acted up when hot. Found out that after sensor broke down completely.

 

Vauxi, my hat’s off to you. Finding the cause of an intermittent fault is one of the most difficult things on these cars.

 

Mine went out last summer while on a road trip. Fortunately, I was visiting a friend that has an XJR, so we took it to his guy and he did all the tests mentioned above. All was good except for the compressor clutch.

 

Try Climate Control Panel 'self-test'?

 

I have to admit I did not know that test was even there.

 

And I somehow always assume that asker is allready knowing this stuff. Maybe this is a car mechanic's mental problem assuming that anyone can do stuff like this.

 

Yes Vauxi, these forums are compendiums of knowledge as regards these cars, however necessity is often
the best teacher. A given procedure may not be examined or even looked for, until a need arises.

 

Thanks for all the info. Since I was out of town I had to take it to a euro car shop. Ended up being bits of insulation blocking blend door and bad heater valve. They had to pull the dash, console and drop the steering column to get to all of it. Thanks again.

 

Yes indeed, that foam will break down over time, and as it disintegrates, plays havoc with
the air flow design. Getting to where the problem is and extracted is difficult and time
consuming. That foam was never intended to last this long and the engineers seem to
have been clueless as to the issues it would cause.