LeRox

ok dramatic title yet still need help/opinions/suggestions on where to look next.....

blew warm air when a/c was not on when I got the car... thought this was normal since when the a/c was activated, felt like it was throwing out ice cubes for years and all was good...

this spring, still warm air entering cabin and when activated a/c, not as cool....

thought it was heater control valve (hcv), checked hcv and diaphragm still intact
and zip tied closed.

ran car, still warm air entering cabin....

had a/c recharged, using 1/2 can r12 and was cooler but not cold....

decided to turn on rear a/c and to my surprise it blows ice cubes....

I've researched the 928 a/c forms and before I start eliminating the possibilities, hopefully someone here could chime in on the possibility's and give an idea of what the culprit may be.

any ideas would be appreciated.

thanks in advance!

Speedtoys

Dying expansion valve up front.

dr bob

What Jeff said.

Or:

1 -- Heater control valve passing hot water to the heater core
1a -- Heater control valve leaking while closed
1b -- Heater control valve vacuum problem
1c -- Other vacuum leak in HVAC system

Diagnosis is fairly simple. Start the car from cold, and immediately turn on the AC. Is it cold? If so, the expansion valve is fine. Then, as the engine coolant warms up, does the center AC vent temp also go up? If so, you are chasing the heater control valve passing hot coolant. Just need to figure out your abc's. Diagnostics are at several tips pages. Start with Wally Plumley's 928 HVAC primer from the 928GT.com website. If needed, the vacuum system diagnosis is also detailed at John Pirtle's 928 tips page.

SQLGuy

Dirty front evaporators have also been mentioned recently. Wouldn't necessarily make center vent air warm, but might reduce flow.

safulop

Not to hijack this thread (but I'm going to anyway),

my center vent blows a tiny bit of hot air always from the lower left corner of the vent (AC off) even when all other air coming out is cool or outside temp. With AC on this goes away and the air is cold. Is this a symptom of anything? My shop didn't think it was or they didn't really notice it. I asked them about the climate control and they tested it and said it was pretty OK, I should be satisfied with it because it will never work as well as a modern system.

Could this bit of hot air (only when car is warmed up) be from the HCV leaking?

-Sean

Bill Ball

Yes. Not a big leak but a leak just the same. I had this for years, was told it was not a leaky heater valve by someone who should know. Wrong. If the air through the vent is hotter than ambient then the valve is leaking. The exception to that is in the first minutes after restarting a warmed-up car. The heater valve OPENs when the car is stopped and takes 10 seconds or so to close once the engine is started. After that, the center vent should approach ambient. Mine was 10 degrees warmer than ambient until I changed out tha valve.

LeRox

Thanks Jeff and I'll research expansion valve.

Dr., I'll go thru your procedure and report back!

Thanks again all for replying!

WallyP

Make sure that the rubber seal at the rear of the hood is present and in good condition. If it is missing, hot air from the engine compartment will enter the HVAC system.

The quick check that dr bob suggested will help determine if the heater valve is leaking, but a missing or damaged seal will give much the same results.

Time to become knowledgeable on the HVAC system

safulop

Yeah that's what I thought, but service records show the PO replaced the HCV a few years and a few thousand miles ago. Thought it should last longer than this, but, well, hot air is hot air. Will put on list of less urgent things to do. It's amazing how stuff goes bad more quickly from lack of use on these cars.

-Sean

dr bob

Sean--

It's probably time to just zip-tie the HCV closed, and leabe it that way until sometime in late October when you start to need a bit of heat for that long morning commute.

I do mine in late June or early July when we finally get into reliable summer temps. I noticed the heater was working this morning with slider set at 70º and the driver's window open. When we get to more serious offshore wind patterns around July, I'll want the heat to stay outside.

safulop

Well, with any luck I'll be driving this car to Calgary in a short while---have to order my spare #53 relay soon, just in case. Up there, you sometimes want heat even in midsummer! Plus the leak, if that's what it is, is not yet affecting the coldness of the AC from what I can tell, it is plenty cold.