mx22

I swear I saw this topic just a couple of weeks ago, but can't find it now. My car had a broken AC when I bought it and I finally had it checked out. Replaced expansion valves and drier. Also, PO had temperature sensor removed so I had it replaced. Now everything works, but back AC is noticeably colder... Does anyone still have a link to that topic?

Thanks!

Glenn M

Close off the heater control valve under the air intake, can use zip ties. You may have the vacuum actuator behind the pod going bad and it is mixing heat in.

You may also want to clean out the evaporator, Auto Zone now carries the spray cleaner. I went to the local HVAC place and got a can.

Good luck!

soontobered84

Block off your footwell flap as it is allowing hot outside air to mix with your nice cold air from the A/C. That is why your front A/C is warmer than your rear A/C.

Bill Ball

The heater valve is the likely suspect, as already suggested. However, if it is providing heat when it shouldn't, then the center vent would be warmer than ambient when the AC is off as well. It's normal for the center vent to be warmer than ambient for a short time on a warm restart, as the valve opens with the engine not running and takes 15-20 seconds to close after start up. But after driving for a few minutes, it should be very close to ambient (compare hand out the sunroof or window versus the center vent). The heater valve itself can fail with either a bad vacuum diaphragm or leaky shutter inside, or the vacuum to the valve may be compromised by a leak anywhere is the lines leading to it or to one of the other actuators. There are write ups on removing and checking the solenoid pack in the console that distributes the vacuum to the actuators. Finally, the "mixing motor" can fail and prevent the heater valve from closing by not relaying the electrical signal to the solenoid that controls vacuum to the heater valve.

It is possible that the front expansion valve is partially blocked, but rule out the heater valve first.

dprantl

This could be due to one or more of the following:

- Heater valve problem
- Fresh air flap problem
- Front expansion valve blockage (rare)
- System is low on refrigerant due to leak(s)

Dan
'91 928GT S/C 475hp/460lb.ft

benny65

Did you do the fix yourself or done at repair shop? Looking to get my A/C check out.

IcemanG17

x2 Bill and I fixed this same issue years ago on my S4...

jacal128

Just fixed mine with the same issues, new heater valve and hose = cooler air on mine.

mx22

Digging this up from the grave - not much free time and when there is some, too lazy to do it... Is there a write up somewhere here on how to diagnose and fix the heater valve?

Thanks!

JPTL

Hi Alexei,
This is what I suggest as step 1 to troubleshooting what's going on here:
Temporarily replace your heater valve with a generic shut off valve (petcock).
These are cheap ( or NAPA BK 6601413 ), easy to install and very basic (either full on or full off). Since they aren't vacuum actuated, you're not only bypassing a possibly problematic heater valve, but a possibly defective vacuum system.. for now.
Once installed, if you get noticeably cooler air coming from your front vents, you've identified the problem as either being a defective heater valve (my guess), a vacuum leak or an issue with your heater control. You'll also have the opportunity to test your original heater valve, which tend to either warp or drop their gasket. Simply hold it in the closed position and run some water through it. If it dribbles the least bit, it's shot. This really is the best case scenario.
If the petcock does the trick and things cool down, you'll have tolerable temps. in your cabin for the Summer, so long as the rest of the AC is in good operating condition.

I say 'temporarily' install the petcock for the Summer to get you by, since you probably won't be needing any heat in your cabin - at least for a few months. When the Winter rolls around, you'll have to replace the petcock with a vacuum operated unit so that you can moderate the temps in the Fall and Winter.

For heater valve replacement, I suggest nothing but the oem unit. Here's why:
The plastic oem unit is unique in that it's a guillotine valve. It requires less vacuum to fully close than aftermarket plunge valves. I've tried a couple of aftermarket plunge valves and they didn't close completely..due to their needing more vacuum than my system was providing.
The oems aren't as stout as the aftermarket metal units, but they won't break the bank. So big deal if you need to replace it after 5 years?

mickster

Here is everything on HVAC from Wally Plumley:

http://www.928gt.com/t-wallyhvac.aspx

Here is John Pirtle's write up:

http://members.rennlist.com/pirtle/svc.html

Alan

If you have good reason to suspect the water valve - try wiring it shut first - if that fixes the problem you have either a vacuum issue in the line or in the actuator - diagnose & fix. If it still seems to be leaking hot water when wired shut you need a new valve - cheap - so just replace.

Alan