jim912928

Took the car out of storage (fired right up). But the climate controls stuff seems not to be working. The center vent will not open/close in any position. And it appears that in any position heat is coming out of the door vents.

Where should I start looking or what could be the cause? Electrical? Vacuum?

deliriousga

Heater valve. It's probably stuck in the default open position and keeping the heat on all the time. It's located under the air filter box. Easy to replace in about an hour. Make sure you get the metal replacement and not the original plastic one. The metal one is about $10 more, but you'll never have to replace it again.

Good luck!

chaadster

although I have not BTDT, it sounds like a vacuum issue; a leaky servo in the dash would mess up all of the vent operations (if you find one bad, disconnect the line and cap it, the other functions should return) and would prevent the heater valve from staying closed (default-- i.e. no vacuum-- is open), which in turn would let hot coolant cycle continously.

could be a microswitch contact issue in the temp slider (copper contacts can be bent back into tolerance), but I'm not sure that would prevent the flaps from working... I could be wrong about that, though, so if I'm wrong, chime up, guys.

Randy V

I'm guessing you haven't tried an archives search yet. The above suggestions are good ones.

the flyin' scotsman

Jim....as John mentions the hot water valve is the most likely suspect and is reached by removing of the air filter box. You can excercise the arm that closes the internal valve and that may cure your issue. Once you've moved it a few times start the car with the heat setting at the coolest position and with the air box still off see if the valve arm has moved. If it has not pull the vacuum line and check for vacuum presence. If you have vacuum the valve is gone and shall need to be replaced. No vacuum then you need to do further research and I would point you in the direction of John Prittles site for detailed testing.

deliriousga

The heater valve is a vacuum issue like chaadster said, but it's due to the plastic insides. The rubber seal slips off of the diaphram as the plastic parts erode/warp over time and gets stuck in the valve. It makes the valve stick so the vacuum cannot close it. Hot water flows all the time and the heat never stops. I'd definitely check the valve before spending alot of time on diagnostics. It's the most common problem with the heat staying on you'll find througout the forums.


If it's not a daily driver, check the valve before you order one. If it is a daily driver, it's only $25 for the better, metal replacement valve and you will have the problem one day with the original valve if that's not the cause right now.
Heater Valve & Vents Problem: http://www.nichols.nu/tip156.htm


If it turns out the valve isn't the problem go through chaadster's diagnostics and here are a couple of more from some sites:

Outside Temp Sensor: http://www.nichols.nu/tip584.htm
Temperature Regulation Failure: http://www.nichols.nu/tip157.htm
Vacuum Failures: http://www.nichols.nu/tip024.htm

chaadster

Even if the hot water valve has failed for mechanical reasons, if his system was operative, he could select to move the hot air to different vents, but as I read the original post, he only has heat at the door vents.

Again, what is the connection between the inop vent selections and the heater valve? A vacuum leak at the valve?

Jim912928, Wally Plumley has published an HVAC paper to help understand and troubleshoot the system; I can forward you a copy if you shoot me a PM with your email, or, of course, you can PM Wally himself for it. You'll probably find it helpful.

the flyin' scotsman

Chaad........the connection between an inoperative valve and vent selections could well be the vacuum HVAC system. The system receives vacuum from a source near the brake booster the black line, that goes into a distribution block under the centre console. The vac disti block recieves input from the vent selction control, opening and closing solenoid valves thus vacuum to the respective valves one of which is the hot water valve. Reference WSM Vol 4 pgs 87-104 thru 87-107.

jim912928

To clarify...with all the controls to the left I still get heat out of the doors. If i put the levers to the far right for defrost I get heat out of my defroster vents. My center vent is closed and will not open at all. So, center vent is inoperative and heat seems to be flowing freely. The climate control module (sliders etc.) was replaced by the previous owner when I bought the car about 4 years ago..so that part is fairly new.

chaadster

I'm aware of that, and that is why I said it sounded like a vacuum issue!! To rephrase my question, is there a hot water valve failure mode that causes inop vent (flap) controls? Again, as I said earlier, mechanical failure of the hwv would not result in inop vent control; might, though, a vacuum leak at the valve cause it?

WallyP

The most common failure in the 928 HVAC system is failed vacuum actuators. Since the vacuum supply line is very small, one failed actuator can make the entire system misbehave.

First, check the small black/blue check valve near the top of the vacuum brake booster, and make sure that you have good vacuum coming out of the valve. Check the four-way connector near the check valve for cracks. There should be one line running to the front fender for the vacuum reservoir and the cruise control, one line running into the firewall to supply the HVAC system, and one plugged leg.

If this doesn't fix the problem, remove the driver's side panel from the center console. Find the bundle of colored vacuum lines. Get a few inches of rubber or plastic tubing that is a snug fit on the vacuum lines.

Use a sharp razor knife to cut the orange line. Apply vacuum to the end that runs up into the dash (not the end that runs forward to the solenoid manifold). If it holds vacuum - it probably won't! - splice the line back together with a short piece of tubing. If it doesn't hold vacuum, plug the other end - the end that runs forward to the solenoid manifold - until you can replace the actuator or its diaphragm. No need to plug the end that runs up into the dash.

Repeat on the green, blue and yellow lines. Don't cut the white (heater valve) line or the black (supply) line.

Once you have good vacuum on the system, check the heater valve for proper operation (off when vacuum is applied), and replace it if necessary.

jim912928

Thanks all, I have alot of diagnostics I can do this weekend! Even with the heat on...I had a blast finally driving it after our crappy winter here in Northern IN!

928drvr86.5

LOL, i just worked on this problem last night on my 86.5 using a good write-up by Wally P that i found on the Nichols site. I was having problems with my heater valve not closing (overiding the AC). Since your center vent is not moving i would guess that the problem is in the dash someplace. There is a small vacuum manifold in righthand side of the driver's footwell behind the plastic cover. Coming out of the manifold are a series of color coded vacuum lines. In my case the orange line was leaking, the one controls the center vent. On my 86.5 the leak on that line was bad enough that it was robbing vacuum from the other lines and it prevented all the rest of the vacuum actuators from working including the heater valve which is the white line coming out of the manifold. After plugging the orange line where it goes into the manifold everything worked (except the center vent will not close now .. obviously). The black line is the supply line to the manifold all the other lines are feeding one thing or another. I would check these vacuum lines first before replacing the heater valve!

Ben Burris

86.5 Indischrot AT #1459

deliriousga

Whatever it ends up being, please post it here when you've figured it out. That's the most helpful thing you can do for the other rennlisters.

jim912928

Hi, I didn't get alot of time today to run all these vacuum checks...only had about an hour so this is what I was able to do:

Vacuum:
1. inspected the spider fitting in the engine bay...no cracks
2. pulled the check valve and heard alot of de-compression...so there was good vacuum at least up there

I then proceeded to remove the access panels on the drivers side footwell to do the vacuum checks....what a mess in there. There were alot of vacuum lines (black, 2 white, red, orange, blue, maroon?). They were all really tight so I couldn't pull any out of the little rubber connectors. So I had to stop there

I then thought about checking the air flow (defrost, center, floor) with the temp slider. So i warmed the car up and did these tests (it was cold here today so this worked well):

1. temp slider all the way to the left (coldest setting)
2. moved the directional slider (eco, auto, bi, defrost) through the eco, auto, bi areas
3. only got air flow through the windshield and door defroster vents
4. air was cold

I then move the temp slider all the way to the right (hot)
1. everything was the same as above except I now got hot air

I then just tried the defrost position and got high fan and hot air. When i put everything back to coldest settings air turned back to cool air.

So, does this sound more electrical in my climate control box?