A/C and heat went out at the same time

'96 XJ 4.0 here and my A/C and heat both went out at the same time apparently. Air still blows and the engine still changes idle speed when the a/c is turned on, so it seems the compressor is still working and coming on. Coolant is full at the radiator cap and the reservoir.

There's a hydro valve/switch where 4 coolant lines connect back by the firewall, up high passenger side. I think this is where hot coolant gets diverted into the heater box in the cabin. I believe I replaced this a couple years ago but not entirely sure. With my limited knowledge this is where I would look first but I really don't know.

How can I test if this valve is still working correctly? Also, where else would you guys look for the source of the problem?

So everything works except the temperature knob? If that's the case, I would check the air blend air door in the bottom right of the air box. Heater and evaporator sit opposite each other on the right side of the air box. The temperature knob acetates a cable that swings that door left and right for the air mix you want.

Sounds like the door linkage may have broken. Is the AC line cold by the firewall?

Well apparently I made a mistake somewhere but the temp adjustment seems to be working ok now. There is an audible thump (familiar sound) in the dash when the lever is moved quickly so that's probably the temp mix door closing and opening. Dunno why this little anomaly seemed to occur but I'll just proceed on from here assuming that the door works fine and the a/c is the only problem.

After running the a/c for 10 min I felt the two lines going into the compressor and neither felt cool at all. Although like saying before the engine idle speed does change when the a/c is turned on in the cabin...indicating the compressor is turning on I suppose...but don't really know.

I've owned the old XJ for 9 years now and never a problem with the a/c. Haven't even noticed it getting slightly less cool...just all of the sudden no cold air.

So I guess the next step is to check the a/c 'freon' (whatever it's called) pressure? And then re-pressurize if needed? I'm assuming it wasn't a slow leak as I never noticed the a/c getting gradually weaker (less cool). Is a system pressurization test warranted before any 'freon' gets put in?

Having a set of gauges makes it easier to troubleshoot A/C. You might have a slow leak and are low on charge. If you have insufficient airflow through the condenser (weak fan clutch) you will probably have less than stellar A/C performance as well.

The manifold gauge set looks like this:

http://www.amazon.com/Mountain-8205...&sr=8-1&keywords=a/c+r134a+manifold+gauge+set

Yeah, just because you're charged doesn't mean you have differential. Sudden leak, or your compressor may have experienced the silent death.

Also look at the compressor, does it appear to be spinning as fast as the belt? A slipping clutch will still get cool *sometimes.

Here's the update...

(Please ignore the title of this thread...only problem I'm having is with the a/c now)

Probably need to spring for a set of refrigerant gauges but to get away with doing it on the cheap I just got a can of refrigerant from the local parts store and used that gauge. Turns out, although I assumed I had a leak just about the opposite is true...my system pressure appears to be too high. Not sure how that happens.

BTW both lines leading to the compressor are the same temp, neither hot or cold. Each is just slightly warm I think b/c they're in the hot engine compartment.

Thanks for all the advice so far. Any advice on where to look now with this new info in mind?


[Overland...thanks, I'll have to check on that and report back next entry]

Forgot to add that my serpentine belt just started to squeak. It never has before and seems tight, so dunno if the two problems are possibly related.