944 Heater Vacuum Troubleshooting

[Tiderfish]

Greetings!

I Hope the day is treating you well.

I have a 1986 944 Base, with the dreaded heat always on issue. I have researched the problem and it seems to either be caused by a broken plastic tab in the kickwell, or cause by a dry rotted vacuum line under the hood. (Per Clarks)

So I poked my head under the driver's side kickwell, and didn't see any broken tabs on the metal rods for the blenders. Then I popped the hood and looked where the image on Clarks and I do not know what is what.

Can someone help me ID what all these lines are for? Or at least tell me what one is for the heater blender?

Thanks in advance!

Matt|ttaM
1986 944 Base (stock)

[Tiderfish]

It didn't seem to want to post my image

[Tiderfish]

[djnolan]

Hello, if you are referring to #8 on the clarks diagram, it is a black plastic cannister about the size of a coffee mug and it has two plastic nipples on it that should be connected to vacuum lines. Sometimes the nipples break off but you may be able to push the vacuum line on to the broken tube and get it to work.

When you upload pics make sure it says completed and there is link to the pic added to your post.

[mikepellegrini]

Here's a good video on diagnosing HVAC problens in late 944's. https://www.youtube.com/watch?v=GjD0FqCNxIo&t=1s

[Eskozki]

My experience is that even with full vacuum on the heater valve it is not 100% tight and some flow of hot water makes its way to the core. Check that the heater flap moves correctly. If the flap doesnt close properly there is enough airflow through the heater core you will be grilled alive. I had similar problem last year. the heater flap had to move only about 1cm more to close and I was no longer cooked alive.

[Tiderfish]

Thanks all for your assistance. I will check all those vacuum spots this weekend.

As for testing the blend door actuation. Do I just stick my head down on the drivers side kick well and turn the knob to see if the rods are moving?



https://drive.google.com/file/d/1UVM1Go9mfSnExSR9jKU8fHwkOoISddQ6/view?usp=sharing

[Eskozki]

Yes, stick your head to the footwell and look that it moves the full range. No need to see the movement. I checked it by gently pushing up and down on the rod to verify it was on the mechanical stopping point when the knob was on full cold and hot position.

[Jfrahm]

I've had every heater problem other than the clip.
Couple cars had bad valves that leaked hot water even when closed. I replace with Audi 5000 metal valves rather than the Porsche valves for a variety of reasons, those have been 100%.

Most recent issue is a slight vacuum leak through the control solenoid causing heat during high vacuum conditions, like at idle. the valve would open at idle, overwhelming the AC, then close when driving.

[Monkey Wrench]

in volvo's the flow thorught he heater core is controlled by a thermocoupler. they tend to freeze up. they can fail, I've taken the thermocouple from a Mercedes before and it was the same part. a quick and dirty fix is to stick a water tap in the hose to or from the heater core and then you can open and close the flow through the heater core manually but you have to stop and open the hood to open or close the tap.

Volvo also uses a system of vacuum controlled mechanisms to control the heater flaps, a leak will mess the system up. in a volvo 740 they hid the vacuum reservoir inside the front bumper , of all places.. in a 240 it's in the passenger footwell. in some cars they have buttons that can direct the flow of vacuum to various actuators and the actuators seem to stand up well. the porsche may have a sliding valve thing that can fail and leak in the dash.

i have a friend with a dodge charger and in that they use these silly mickey mouse made in china motors and the plastic gears keep stripping. It's a terribly cheap idea that fails. the shop quoted him some ridiculous price to take the plastic dash all apart to change them.

[Tiderfish]

Originally Posted by mikepellegrini

Here's a good video on diagnosing HVAC problens in late 944's. https://www.youtube.com/watch?v=GjD0FqCNxIo&t=1s

I have reviewed this troubleshooting and determined the blend door motor he actuates does not actually do anything. If I listen real close, I can hear a quick blip like it receives power and is jammed. I believe I have isolated the motor/actuator responsible for this flap door. I would post a picture, but this forum does not seem to like me doing that.

[Tiderfish]

Originally Posted by Jfrahm

I've had every heater problem other than the clip.
Couple cars had bad valves that leaked hot water even when closed. I replace with Audi 5000 metal valves rather than the Porsche valves for a variety of reasons, those have been 100%.

Most recent issue is a slight vacuum leak through the control solenoid causing heat during high vacuum conditions, like at idle. the valve would open at idle, overwhelming the AC, then close when driving.

I am very interested in getting this metal valve. After a quick search, I see a lot of choices for the Audi 5000. Can someone please narrow it down with a part number or a year please?

[Tiderfish]

I have finally gotten some time to troubleshoot this problem. First off thanks to all for your help!

Step one was locating the vacuum cannister under the hood. I found it, and after years of wondering what that was ( I even removed the battery to fiberglass the rust spots under it) I know what that thing is. Since it the nipple was pointed down, I never saw that the LINE WAS DISCONNECTED.... Reconnected it, and took it for a spin. Still the heat persists.

Step two was watching and repeating the steps in the video posted by @mikepellegrini

I was not able to trigger the heater actuator to move. To be sure, I uninstalled the dash trim, and center vents, to watch the door move. Nothing.

I then pushed the door open and closed with my hand, and watched the happenings on the rods below, and noticed that the arm with the slider on it moves freely. After seeing this video, I assume that is normal.

https://youtu.be/7O5XCKcFPw8?t=106

In this section of the video you can see the inner workings of the HVAC module. The door he operates here does not open unless I manually press upon it. You can also see the arm that has the slide pin in it I am referring too above.

I saw another video where a British bloke pulled off that motor assembly the slide arm is attached too and found the actual motor was seized up by years of rust. He was able to clean it up and get it to work again. I am going to try this next.

I am also going to double check that there is vacuum being generated at the cannister, and that the valve actually works.

My question is this. Where is the motor, and actuator that is controlled by the heat knob?

How can I troubleshoot to make sure my heat dial is actually telling the blend door to open? (measure resistance on the logicon (hvac) unit? If so what pins?

Is it even a blend door that is keeping hot air form from being pulled through the heater core? Or is that solely done by the vacuum diaphragm valve under the hood?

Thanks again all for reading this and any help is appreciated!

Matt|ttaM
PS if anyone knows why I (a "pelican rookie") can't post images, please let me know. I am doing the posting part right, I have done the same on many other forms that use the same code. Perhaps I am too new to the forum?

[djnolan]

My drivers side bled door motor was totally seized by rust and I had no heat. When I tried to remove the motor the plastic cracked and the motor broke free of the housing. I was able to move the door linkage to keep the door open so I had heat in the winter and cold air on my feet in the summer.

I am not sure if these motors are replaceable or not.

[Jfrahm]

Re: pics, I assume there is a delay before you can post to reduce spam but you might also try posting something very small. That said I just tried to post pics and got this warning:

"You attempted to upload a file totaling 373892 bytes. We tried to compress it down, but it still exceeds the maximum limit of 200000 bytes. Please go back and select a smaller image."

Anyway I resized the images down to postage stamp sizes and they uploaded.

Re: heater valves, I've used both of these, more often the not all-metal one but it's crimped together in a way that's less likely to crack in half like OEM (in my opinion).

[djnolan]

testing image upload

Go to "go advanced" , click the blue "click her to upload photos" button, select file, and wait for it to finish uploading and to place an IMG link in your message before clicking finished. NOTE: Images must be less than 5 Megabytes in size, this one is 3.5MB

[Tiderfish]

Thanks for your help guys. I found the partially metal and plastic unit on scamazon for ten bucks. Ill try that one. I manually actuated the one on there and it has resistance, like it is pushing air in the diaphragm, and slowly releases the pressure, so I don't really suspect it at this point.

I am now wondering if the control solenoid is working correctly. Cause my thought is, that since the coolant control valve stays open, the signal must be "getting lost" on the way to it. So my question is now this: where are those solenoids located? Are they under the passenger side of the dash?

As far as the driver's side motor being seized, that only moves the flaps right? It does not control the heat, right?

[Tiderfish]

Lets see if this image is posted...

Here is the motor I believe to be seized.

[Tiderfish]

Actually I think it is the one on the bottom (left in this image) that is seized.

If I understand correctly the video posted above is trying to manually trigger this motor, but it does not work.

[Jfrahm]

If the heater valve is closed and not leaking coolant through internally (which has happened to me) there is no hot water to cause cabin heat regardless of solenoids, flaps, doors, etc.

You can observe if it's closed and if not you can force it closed and wire it in that position to see if the heat cuts off. Obviously vacuum should close it and when closed it should not leak but it's still good to test/confirm those cases.

You might need a ziptie, twist of wire or bit of heat shrink to secure the stock vacuum line onto the new heater valve. Most of these seem to have a smaller vacuum barb than the Porsche one.