heating problem

[georges 928S]

Hi again, when i turn my heater on while driving and then shut it down, i still get

heat like its all the way on speed,dont want to shut off. any ideas. Ed.

[MPDano]

Is the heat on all the time? Even when you have the temp slider to cold? If so, your Heater Valve (just behind the Air Filter) is bad. The rubber diaphragm goes bad and the vacuum can't close the valve. Which also causes a vacuum leak.

[georges 928S]

Mr Danno, thanks for your reply, yes heat stays on even when slider is off. should i replace the diaphram or replace it with new one. Ed.

[harborman]

Replace the entire valve only about $20.

Mr Danno, thanks for your reply, yes heat stays on even when slider is off. should i replace the diaphram or replace it with new one. Ed.

[MPDano]

Originally Posted by harborman

Replace the entire valve only about $20.

Yup, replace the whole enchilada. I don't even think you can repair just the diaphragm.

[MPDano]

Also, I know this has been said before. Put the Year of your 928 S in your Signature or Profile.

[MPDano]

$16.25 here on Pelican

928-574-573-03-M53

Porsche 928 Heating & Ventilation - Page 1

[Mrmerlin]

also replace the short hose with the heater valve these parts should be replaced together.
After this go to 928gt.com on page 2,
look under tips and links and follow Wallys post about HVAC system diagnosis you have other pods leaking as well.

[JK McDonald]

Hey georges 928S, There have been a few times when Miss Purdy (84 Model) will occasionally hesitate to make the transition from heat to no-heat while moving the temperature select lever.

Initially, I had suspected that it might be a defective hot water vacuum shut-off valve or one of the control solenoids. But when I had the dash and the console out for a dash replacement, I checked the integrity of all my vacuum modules, the bank of vacuum control solenoids, all the flaps, doors and pivot points and the interior/exterior thermistor circuits. Then as long as everything was scattered out on the garage floor, I disassembled and cleaned the slide lever contacts inside the console mounted Heat/AC control unit. Strangely- everything was found to be fine?

My only assumption is that the wear and tear on a 20+ year old ventilation system sometimes needs a little time to think things over as you adjust the Heat/AC to your liking. I have discovered (with my car anyway) by cycling the temperature control and function levers very gradually - that my system operates fine (except for when it sometimes doesn’t and I must slowly repeat the command).

Good Luck, Michael

[georges 928S]

Mr mcdonald, what you mean by cycling the temperature control, do you mean sliding it back and forth. Ed.

[JK McDonald]

Hey georges 928S, By cycling - I mean to simply repeat the last movement of the slide control lever. On my car, if I move the temperature control toward the full left (cold) position and the heat sometimes doesn’t shut off - I know to move the temp lever back slightly toward the right and then back to the far left. I suspect that the electrical switching contacts within my console mounted Heat/AC control unit may be a bit worn and sometimes does not complete the vacuum control solenoid circuit properly.

The advice from Mrmerlin and MPDano to start with the hot water control valve mounted on the firewall behind the air cleaner is the best place to start your troubleshooting. This vacuum controlled hot water shut off valve must open/close correctly with no internal hot water leakage or you will never get the rest of your ventilation system to operate satisfactorily. If this valve is defective simply buy a new one.

By the way, Dwaynes Garage Site: www.dwaynesgarage.norcal928

is an excellent place to find lots of good information and experience on the 928.

Good Luck, Michael