riviera455

the car a 1984 928s i bought yesterday has some more troubles.


no heater, cold ventilation works perfekt, on 1, 2, 3,
defroster (fan)does not engage the fan at high speed. relay is checked, interchanged with a spare and ok.
making an elektrical bridge in the contacts where the relais fits makes the fan go on his high rpm, but no heat. the relais does not get his defroster signal.
it might be some valve somewhere in the car,,i think (almost sure)the heatercore does not get warm water. is this a valve that works elektrical? where lockated?
oh by the way, coolant level is fine.
(ac does not work, no belt on defroster,)

76FJ55

The valve is vacuum operated and is located in the engine bay below the air cleaner box on the passenger side. this valve is normally open and when fails typically causes there to be heat even when you the controls are set to cool. the 2 promary failure modes are:1)the seat inside the valve warps and still allows flow in the closed position and, 2) the vacuum diaphram leaks to the vacuum no longer closes the flow. Some owners ziptie the valve closed in the summer monthes to ensure there is no flow. Replacement valves are relatively inexpensive should you need a new one. I would guess that if the core truely isn't getting warm, either the valve is tiptied or the heater core is bypassed.

riviera455

i will check it out, i found allready two soft tubes from the front of the engine going further upwarts to the cockpit, these where hot.so hot water is going somewhere, didnt had the time to look further because the car was outside running and it started reigning

and inside the interior i found a short thin tube with some small plastic one way valve in. it could be a vacuumproblem,i cant hear anything moving when i switch from cold to hot.
i also found a replacement relais for the defroster, so someone has been surching before but did not fixed the problem. i hope it is not a leaking heatercore ,,that would be my second car that i bought with a leaking core. always difficult and expencive to replace.

thanks for helping so fast ,,

Imo000

How about using the search option? This topic thas been discusses dozens of times with detailed write ups.

riviera455

sorry,,
did a verry long search , used "heater", used "no heater" used "only cold air" and many more tags,,nothing useble shows up hundredes of toppics , but nothing that helped me further.
maby ill try ,"only hot air" and then i will have answers,,but "only hot air"is not my problem.

GlenL

The common problem is always getting heat. Not getting heat is unusual.

Some people tie the valve shut. I prefer to run a vacuum line from the manifold directly to it in the summer. I suggest taking a look at the valve and see what's going on. The black hoses could be hot and still not have enough water flowing to be noticed inside the car.

polecat702

Try HVAC system. 928 international web site, Tony's Tips, great write ups with pictures.

Stromius

Might be corrosion & junk in the heater line too. Maybe just flush it gently both ways?

Landseer

Be patient. Got to campaign through the issues slowly.

SQLGuy

My guess would be that the previous owner tied it shut because he was getting too much heat.

James Bailey

Possibly someone has put a plug inside the heater hose to stop all water flow and all heat. Several new owners have found such a "fix " !

VehiGAZ

One never knows what kind of madness lurks in the bowels of a previously-owned shark...

riviera455

haha,,,someone bolt something in the line to close the valve.
thanks, it looks a stock piece, i could have been surching long time.
such a stupid remedie,,i dont like these macgyver solutions,,
now i have to find out why it is not function like it should,,i defenitly want warm air in the morning and cold in the afternoon.
i did a new search and have found lot of info.
the most difficult for me is to find the exact words that lead to the topic i need,,,
i used the words "heater",,"no heater",and did not found anything, but now with "no heat" and , "only hot air" i found it.
englisch is not my daily language,,

a possibility are the vacuumrelais,,or vacuumswitches somewhere deep under the dash,,,grrrrrr not a pleasant job.

GlenL

The basic problem is often a vacuum leak in the HVAC system. This prevents getting enough vacuum to the valve to shut it.

Best of luck!

SQLGuy

These are not too bad to test and troubleshoot... replacement is another story.

It doesn't take very long to remove the left and right side covers from the center console. Once these are off, you can remove the HVAC manifold (where all the colored vacuum lines run) (three screws, but the middle one is a pain to get to).

With the manifold loose, you can pull the individual colored lines out from their vacuum solenoids and use a small vacuum pump to test each circuit for leaks. That will tell you if any of your actuators are leaking. If you find one that is leaking, you can plug that connection to the manifold until you get the parts and time to replace the actuator... that way, at leas the other functions, such as the heater control valve, will work correctly.