Heat through Door Vents?

[MPDano]

I was driving to work this morning and felt heat coming through the door vents. I didn't feel it coming from any other vent. I am still trying to sort out my A/C issue so I am wondering if this is related? FYI, I had nothing on (A/C or Heat).

[morriss]

I am in the same boat Dano. However, none of my climate control operations work right now. Just hot air blowing through those door vents. I have simply shut them for the time being, until I get to the AC problem. Other issues are taking precedent right now. I am curious to see what info others respond with. Off the top of my head it sounds like a flap issue; one of them opening when when it should stay closed, that is until you push the lever over on the temp. setting over a little. The flap should then open a little to allow the hot air to mix with the cool air from the AC, thus making the air coming out of the center vents warmer. Just guessing though.

[MPDano]

I hear you. I was thinking the same thing. I hope someone will chime in with some suggestions. I just got home and man was it hot in my car.

[morriss]

Hey, read Alan's response to Yoni in "Ventilation Question."

[tedward515]

I run into the same thing on my 81. If I have the vent on, I get cool (thats relitive in Florida) air from the center and lower vents but hot air form the door vents. I haven't thought much about it myself either, as I have other things to work on. I am very interested in what others may have to say.

[Dozman]

Wally P has an excellent write up on this area. Give him a shout.

[MPDano]

Originally Posted by Dozman

Wally P has an excellent write up on this area. Give him a shout.

His user name doesn't come up in the searches. Do you have a link to this write up?

[Glenn M]

The vacuum actuator behind the POD will cause this, been there done that.

Glenn

[MPDano]

Originally Posted by Glenn M

The vacuum actuator behind the POD will cause this, been there done that.

Glenn

There are multiple behind the center console, so behind the "POD" there is just one? Possibly bad diaphragm?

[Dozman]

Glenn I have an email addy. but hate to give out others emails.

I know DR at 928 specialists can give you his email.

If you go on the other site. He is on there. Tomorrow, I will look on my desk top for the doc. If I find it I will forward it. No matter what wally gets the kudos for his wisdom he had written down.

[Mrmerlin]

go to www.928gt.com and find page 2 then click on tips and links.
Then you will find Wallys info RE HVAC system operation.
Also you can google 928 keepers

[Yoni_d]

Where is the location of the Fresh Air flap?

[MPDano]

Originally Posted by Mrmerlin

go to www.928gt.com and find page 2 then click on tips and links.
Then you will find Wallys info RE HVAC system operation.
Also you can google 928 keepers

Great source! Firefox NON-friendly by the way. I am posting some great info in a quote. I especially like how he broke down the actuators by hose color.

THE HVAC VACUUM SYSTEM





THE VACUUM SOURCE



The vacuum source for the HVAC system, as well as the cruise control on earlier cars, is a very small line coming off of the vacuum brake booster check valve. A 1" diameter black/blue check valve a couple of inches down the small line is intended to maintain a high vacuum level in the system. Next on the line is a rubber four-way connector. One leg is the inlet, one is blocked, one goes to the left front fender for the vacuum reservoir and the cruise control (tempostat), and the last leg goes thru the firewall to feed the HVAC system thru a black line.





POTENTIAL PROBLEMS



The small vacuum check valve rarely fails completely, but it is all too common for it to fail partially, limiting vacuum flow. This would be no problem if the entire HVAC vacuum system was leak-free - but it almost never is. The check valve has also been know to cause a very irritating and hard-to-locate buzzing sound if there is a leak in the system.



The four-way rubber connector can develop cracks and leaks at the point where the legs join.



The plastic vacuum reservoir can develop leaks.





TROUBLESHOOTING THE VACUUM SOURCE



One of the tools that is almost required for HVAC maintenance on a 928 is a vacuum tester. The most common - and one of the best - testers is called a Mity-Vac. It is a gauge-equipped hand vacuum pump, and the kit includes several adapters and sometimes a brake-bleeding kit. The tester is available in both metal and plastic, with the cheaper plastic version acceptable for most 928 owners.



Using the Mity-Vac, remove the small blue/black vacuum check valve, and test in both directions. There should be very free flow toward the brake booster, none in the other. If you don’t have the tester, you can use mouth vacuum, but be careful to avoid inhaling any fuel or fumes.



Using the Mity-Vac, test the line going into the left front fender - it should hold vacuum indefinitely (it will take MANY pumps to pull a vacuum, as you are having to empty the reservoir). If not, find and fix the leak.



There should be a strong vacuum at the line going into the firewall to feed the HVAC system. Be sure to check the rubber connector carefully for cracks.





THE VACUUM CONTROL SYSTEM AND ACTUATORS



The black vacuum feed line runs to a vacuum manifold, located inside the center console, just forward of the radio. There are six electrically-operated vacuum solenoids on the earlier cars, five on the later cars. Each of these solenoids feeds a vacuum actuator.



In the earlier cars, these are (left to right):

Footwell Flap - Yellow Line

Defroster Flap - Green Line

Center Outlet Stage I - Orange Line

Center Outlet Stage II - Brown Line

Mixing Flap and Heater Valve - Red Line

Fresh Air /Inside Air Flap - Blue Line



On the later cars, these are (left to right):

Footwell Flap - Yellow Line

Defroster Flap - Green Line

Center Outlet - Orange Line

Heater Valve - White Line

Fresh Air /Inside Air Flap - Blue Line



The function of each of these is obvious from its name, except perhaps for the two-stage actuator on the Center Outlet on the earlier cars. This was simply an attempt to fine-tune the air flow so that you could have more air to your feet and less air from the center outlet.



One point on the heater valve - the flow of hot water to the heater core is cut off by vacuum, not turned on by vacuum. This means that the failed condition is heat on.





POTENTIAL PROBLEMS



Oh, yes. In many owner’s opinions, the vacuum-actuated HVAC system is one of the few real design flaws of the 928.



The most common problem is leaking diaphragms in the vacuum actuators. In fact, very few 928s do not have this problem to some extent.



The electrical portion of the vacuum control system rarely gives problems.





TROUBLESHOOTING THE VACUUM CONTROL SYSTEM AND ACTUATORS



Again, the Mity-Vac tester is a virtual necessity.



Testing the vacuum system is simple in concept, slightly difficult in execution. You just apply vacuum to each actuator with the Mity-Vac, and see if it holds vacuum or leaks.



It is possible, but somewhat difficult, to move the vacuum manifold and solenoid valves out enough on the driver’s side to access the vacuum lines for testing. The unit is retained by a screw on each end. If you do this, be careful to ensure that none of the vacuum lines or electrical wires are displaced during re-installation.



It is easier to cut the colored plastic vacuum lines for testing, splicing the cut ends with short sections of rubber hose afterwards. The most common failure seems to be the center vent actuator. Use a sharp razor knife to cut the orange line, and vacuum test the line running up into the dash. It should hold vacuum. If so, splice the line and continue to test the blue, yellow and green lines. Do not cut the black (supply) or the white (heater valve on the later cars) lines. If the actuator leaks, plug the lower end of the line - the end that runs forward to the vacuum solenoid - until you replace the actuator. It is not necessary to plug the upper end of the line - the one that you tested.



The heater valve is cheap and easy to replace. It is located just behind the engine, under the air filter box. The black end goes toward the engine, and it does make a difference. If it is installed correctly, water flow pushes the valve more tightly closed, if installed backwards, water flow pushes the valve open.

[MPDano]

Ok, that write up was awesome and I am pretty sure I know what all the issues are with my heat and A/C.

Ok, I know I have bad actuators since I ran a vac test to the line going back to the firewall which feeds the vac manifold in the car. No joy on holding vac. Ok, I disconnected line from Brake Booster and blocked it.

Now, my heat through door vents. Write up says fail mode is heat on. Ok, ran a vac test to heater valve actuator and it holds vac great. Ran a line from heater actuator to Brake Booster line. Vac now closes heater actuator valve. "NO More Heat in Car!" Awesome.

Now, flipped on the A/C for giggles. Got COLD A/C air in the door vents and defrost vents. *****en, I know that the vac is disabled so the actuators can't move air to the proper vents.

Now all I gotta do is fix the actuators that are faulty behind the Center Console (diaphragms most likely) and I'll be good to go.

Question though: When I turn my A/C on, I can hear the belt slapping the Oil Pan. I am sure it's on there with proper tension. Does this mean Faulty Compressor, need Oil, or something else?

[MPDano]

SUCCESS!!!!!!!

Drove my 928 to work this morning, 26 miles door to door and "NO" heat from any vent. Love it! Also, seems like my car runs smoother since I discovered that vacuum leak.

Thanks for all the help all!

[psychII]

nice job!

There's nothing like working AC.

You know, I thought my car ran smoother after I fixed the HVAC vac leaks.

Fix one thing, and another pops up.

[orff928]

This was one I couldn't figure out but when I replaced my radiator..it stopped.

[Alan in AZ]

Originally Posted by Yoni_d

Where is the location of the Fresh Air flap?

The fresh air/recirculate flap is right under the blower motor (LHD passenger side between the firewall and bulkhead). It is therefore also directly above the fuse panel in the passenger footwell. You can see the intake.

Alan

[morriss]

Dano- Are the vacuum tests supposed to be done with car running or off? Since my wp is bad, I don't want to start the car. I hooked up the mighty vac and not one of the actuators held a vacuum.

Half of my lines don't either (including the main black line from the booster), the heater valve too.

My second question is, what do you do when the lines are out? Anyone ever replaced these things? The only ones that hold (okay, leak very slowly) are the footwell flap, defroster flap, stage 1, and fresh air flap.

[EIPtuningR32]

i had and still do have this problem with my "girly" R32.... it gets hotter than hell if you leave the air off and you dont have every window down and the sunroof open.