Need HVAC Help!

[cfassett]

Fellow Pelicans, I could use some help.

My '86 951 has some issues with the HVAC system that have me stumped. I've had the car for 7 months, and this issue has been there the whole time. My primary issue is there is no heat. The fan blows fine... well sort of... but there is no heat. Here are the issues:

1- no heat regardless of where you are on the temp knob.
2- fan blows fine, but only when set to 4. Defrost also works on 3 and also 4. No fan when car sits still, and fan set to 1 or 2.
3 - recirculation flaps not closing when setting turned on

So, I have tried a second Control Panel, and the issues are the same. Used hand held vacuum, and got both recirculation flaps to open and close fine. Also able to open and close heater valve with the hand vac unit. The flaps and valve don't close with sgnals from the control unit, though. Only from manual vacuum. So, it seems the solenoids for recirculation flaps and heater control valve aren't sending vacuum.

The arm / bracket with the rod in driver side footwell, from defrost control motor and mix flap control motor do not move when control settings change. Should they? They are also pretty corroded, but the plastic clip is in place.

I guess I'm hoping all of this rings a bell for someone and they can say, "hey sounds like XXX!" or "check this or that"

What does this sound like?

[universeman]

No heat generally means no hot water in the heater core. Did you check heater control valve? it has to open for heat to flow.

[cfassett]

Yes. HCV opens but only via a manual vacuum pump.

[CarGuyNeil]

Originally Posted by cfassett

Yes. HCV opens but only via a manual vacuum pump.

Do you get heat then? If so this could be the issue. The valve isn't opening.

Sent from my SM-N950U using Tapatalk

[kdjones2000]

Look in the Electrical section of the shop manual and there are testing procedures for measuring voltages at the actuators, in order to determine if your control unit is functioning correctly.

My guess is that the vacuum lines in the engine bay, at the firewall, under the heater hoses are not correctly connected, or your vacuum reservoir is disconnected / leaking, or a PO has completely rewired your vacuum connections and messed up your HVAC systems.

[cfassett]

Nope. No heat even with valve opened manually.

[944 Ecology]

1) The fan speed problem is most likely the resistor pack under the cowl.

2) If the blend door motor is not moving when the temp control is rotated, then it may be that one of the thermistors is not reading properly. There are three, all should read the same at a steady ambient temperature. Also, is the linkage between the blend door motor and the blend door connected?

[cfassett]

Originally Posted by 944 Ecology

1) The fan speed problem is most likely the resistor pack under the cowl.

2) If the blend door motor is not moving when the temp control is rotated, then it may be that one of the thermistors is not reading properly. There are three, all should read the same at a steady ambient temperature. Also, is the linkage between the blend door motor and the blend door connected?

Here is a pic of the system in the driver side footwell...



When the car is running, and the knob is turned, nothing moves in this section, at all. It appears to me to be linkage. Sorry... I’m ignorant of this area. Should there be something visibly moving in this area?

[944 Ecology]

Originally Posted by cfassett

Here is a pic of the system in the driver side footwell...



When the car is running, and the knob is turned, nothing moves in this section, at all. It appears to me to be linkage. Sorry... I’m ignorant of this area. Should there be something visibly moving in this area?

Yes, the motor should be rotating and moving the linkage with it.

If it is not, you may have a bad motor.

[kdjones2000]

Look at the debug procedures in the shop manual.

Test the actuator with a small 12V battery, etc....

[9FF]

If the valve isn’t opening like you say, and the coolant system was bled at some time previously with the valve closed, then you have one big air-lock in your heater matrix that’s stopping it ever getting hot. The fan only operating on full (4) is your resistor pack, remove it and soak it in some vinegar and that should fix it.

[cfassett]

I appreciate the help guys! Will post what I find once I can get back out to the shop and spend some time on it again.

[cfassett]

Originally Posted by 944 Ecology

1) The fan speed problem is most likely the resistor pack under the cowl.

2) If the blend door motor is not moving when the temp control is rotated, then it may be that one of the thermistors is not reading properly. There are three, all should read the same at a steady ambient temperature. Also, is the linkage between the blend door motor and the blend door connected?

Resistor pack...



Nasty... vinegar, here we come.

[cfassett]

After a couple hours in white vinegar...



One of the wires seems to have popped loose. Looks like a trip to find some electrical adhesive tomorrow and then pop this thing back in.

[cfassett]

While troubleshooting this, I found this loose connection near the glovebox. Anyone know what this is supposed to connect to?

[944 Ecology]

Originally Posted by cfassett

While troubleshooting this, I found this loose connection near the glovebox. Anyone know what this is supposed to connect to?

That is a connector for a lightbulb. Small, 1.2 watt wheatbulb.

[cfassett]

Still struggling with this.

Frustrated with how complicated this system is. How many of you have decided to just pull the whole HVAC system out of the car?

[Pauld_94S2]

HVAC system needs a source of vacuum to operate doors and heat/cool.

Start with testing vacuum at the brake booster and work downstream from there.

There's a vacuum reservoir (juice cna sized) next to the battery under the plastic cover. Lift gently, you should see. it. Also, visually inspect (test if possible) vacuum lines going into firewall just behind back of engine.

[cfassett]

I’ve been able to operate the heat valve and the recirculating flaps directly with a nightly vac. Hooked the mighty vac to the supply side from engine to firewall yesterday, and it didn’t hold vacuum. Should it hold pressure?

[Pauld_94S2]

It won't hold vacuum on the engine side of the one-way valve but you should have vacuum on the other side, typically at the brake booster.

The one way valve is a blue/white or blue/black plastic part on or close to the brake booster that keeps vacuum for the brakes..