Heater valve never opens to heater core, why?

fiily · 06:30 PM

So I pressure bled the coolant on the new to me 944 and I'm finding that heater valve is always under vacuum(closed) and never opens to allow the circulation of the coolant through the heater core and just blows cold air, as the temp gauge continues to climb on the dash. I also have the usual drivers side heater metal clip broken, and the support rod was just dangling so that is the next to do item.

Am I correct in thinking this part in red bold letters is my fix? The vacuum line looked fine, and when I pulled the vacuum hose off the heater valve, the valve opened.

From Clarks-Garage:

The second problem is with the heater control valve. The heater control valve is vacuum operated and located at the back of engine near the firewall. There is a vacuum line which goes from the valve to a vacuum connection at the firewall where the heater hose connections penetrate the firewall. Check this vacuum line to make sure it is connected and doesn't show any signs of cracking. There is another vacuum line fitting near the heater hose connections which goes to a rubber "Y" connector. One side of the "Y" goes to a small check valve attached to the large brake booster vacuum line at the back of the firewall. The other side of the "Y" goes through the firewall to a plastic vacuum retention canister next to the battery. Make sure all these lines are connected and don't show any signs of cracking. If all vacuum lines are properly connected you may wish to remove the heater control valve from the system and check it's operation with a vacuum tester. A problem with the heater control valve opening may also be caused by the vacuum solenoid valve going bad. Remove the solenoid and apply 12 VDC to valve to see if it opens and closes properly. If you look at the picture titled HVAC UNIT RIGHT SIDE above, the solenoid is component #3.

fiily · 08-03-2016, 06:54 AM

So, I went under the passenger side dash and found that the #9 heater valve solenoid(green arrow) is missing the vacuum line(red arrow) to it from the recirculating valve.

The Porsche PET shows this should be connected via a t-fitting from the recirculating air valve.

This might be my issue, can anyone else confirm on a 85.5 that this hose and t exists on their vehicle from the recirc. solenoid to the heater valve solenoid?

jslo · jslo's Garage

I can't confirm because mine was plundered and bastardized before I ever even got in there to remove it all, but I have the spare parts you need for testing and can bring them (and beer) when I return your flywheel lock - before if then if needed.

fiily · 10:51 AM

Pulled the vacuum hose off of the heater valve which caused the heater valve to open and got coolant flowing through the heater core and heat in the cabin. I ordered (4) metal clips and supports for the broken support and missing clips this car has, and preventative purchases for any future 944's.

The engine temp is still high, hovers @ 3 white temp hash mark @ idle, so I am going bleed the system again since the heater core never opened before and probably has plenty of air pockets. If it doesn't fix the idle high temp issue, then i'll drain the rad fluid/reuse it after I install a new wahler 75deg fan switch/71 deg thermostat, then power bleed the cooling system again.

Hoping the 2 low temp items above fix my idle temp issue, if bleeding with the heater core open doesn't.

The good news is that I recharged the a/c system since it was converted to r134a by the PO and now I can drive the car in the summer months without roasting.

fiily · 08-04-2016, 05:07 PM

So I tested the fan relay and everything tested fine according to clarks garage. The low and high speed fans work via the thermofan switch jumpers.

The low speed fans don't kick in until a tick below the 3rd white line in the temperature gauge.

The high fan speed settings never engaged even @ the 3rd temp line , they only enaged when i jumpered the 1 & 3 positions on the thermofan switch.

Should I replace the thermofan switch or anyone else have any idea's of what else to test?

fiily · 06:24 AM

Pic of the solenoids under the passenger side dash. See the missing vaccum line on the solenoid nipple? The nipple is directly left of the white wire tie.

I also purchased a stant pressure tester and redid the bleeding and found that I had 2 leaks in the cooling system, 1 at the heater control valve, thankfully nothing dripped into the bellhousing/clutch area.

The other was at the radiator neck, both tightened and rebled the system, temp gauge now sits at 1/2 way mark, fans kick in when it goes up and then brings the temps back down to a tick above the 2nd white line.

Seems as if the FLAPS pressure tester is no good for 944's, the stant 270 aka 12270 pressure tester with the A tester is a perfect fit for our cars.

fiily · 05:19 PM

Fixed it after pulling the amp, head unit brains and glovebox.

The Vacuum lines were not connected via T to the heater control valve actuator as seen in the pics above. Stereo installer more than likely accidentally pulled the vacuum line from the heater control actuator and put in a spare vacuum hoses that went back into the heater control valve vacuum line when installing the amp and head unit brains for the 944.

Now I have heat/cool controlled from the climate heat knob once again.