johnf95111

Just to say my peace, all CAPS does make text more difficult for me to read. Leading caps and punctuation helps the reading and comprehension. If I see a long message written using all caps, I won't bother reading it. No read no comprehension no problem.

Back to the real issue:
I'll be digging into my rear AC unit tomorrow. I'll post what I find unless someone else chimes in with some rear temp control details.

This has piqued my interest.

Cheers,

John Fagerlund
'89GT

mackmorrowjr

Thanks guys. I have reached the age Mac is talking about. MACK

H2

ESPECIALLY WHEN YOU'RE BALD CAPS ARE REALLY GREAT.

h2

SharkSkin

alex70

Sorry to hijack the thread, but it seems to fit in with the original diagnosis and prognosis.

The problem I have is reversed: rear a/c blows ok, cool but not cold. Stable at the same temp though for a long time, The front vents have no cold -blower working fne. Head unit overall functional except for the periodic full blow for a minute or two now and then.

I realize from searching (and this thread) that F/R A/C share same freon. I'm a bit confused tho that turned on 'cold' rear blows cool, but front a no-go.

I would think, others might agree that the head unit is functioning, dilemma is what to look for when front bad and rear working ok??

Sorry for the long post.

thanks-

Rich

dr bob

Rich--

It's possible the front AC expansion valve is partially or completely plugged, or it's just non-functional.

Anothetr common failure mode for this symptom includes the heater control valve. If it fails, or the vacuum system controlling it has a leak, the valve goes open and the hot water pours through. You can look at the valve, under the lower air cleaner housing in the engine bay. There's a more elementary test though-- Turn the AC off, temp slider all the way left, blower on. Is the air coming from the vents hot, like heater-on hot? If so, get the heater valve and possibly the vacuum system fixed so the valve will close.

alex70

Thanks dr bob-

I will start with the expansion valve - the heater valve you speak of was recently replaced as was many vacuum items on the top end after intake R&R.

...will investigate further.

dr bob

Alex--

The heater valve may be new, and lots of vacuum stuff may have recent work. What you want to look at is whether the heater valve is OPEN. Doing lots of work and replacing the valve does not, unfortunately, guarantee that the valve will be closed when you want it to be.

docmirror

If the AC shop did the work right, he pumped it down first, then pressure test, then fill with fluid. Given that it worked before, and no one has messed with the wiring in the center console, the tempostat dial should be working. It uses a comparator circuit to check the temp of the coil vs a set voltage from the tempostat dial. Turn the dial all the way to the right(CW), and turn on the blower. If not cold after a few minutes, I would suspect the expansion valve.

If you take the cover of the rear AC, you should be able to access the expansion valve, and give it a gentle tap. the diaphram may be stuck. If it still won't cool, you may have a blockage in the line going to the rear AC evap. The front will still work because the evaps are in parallel. Please don't use all caps, it's annoying.

Doc