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Heater control panel repair with schematics

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Old 12-12-2020, 04:22 AM
  #31  
KAROZZA
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Yes, I believe the CCU environment is quite humid with surrounding heater matrix. In my case the heater matrix drain got clogged & the central vents occasionally "spitted" droplets via the blower at maximum speed, which eventually dropped on to my Becker radio, & in turn shorted beyond economical repair.

It's always good to learn more, so many thanks for sharing.
Old 12-14-2020, 09:11 PM
  #32  
StoogeMoe
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Does anyone know if those TLE4201A motor drive chips are still available? I can't find them on Digikey or Mouser.
Old 12-14-2020, 09:14 PM
  #33  
StoogeMoe
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Oops. Never mind. I see you found some. I was just wondering.
Old 12-12-2023, 12:01 PM
  #34  
Donkeychobo
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Default Is my control unit faulty?

Hi all,
I am trying to fix the climate control (non aircon) on a 1988 944 my son has just bought. Its a UK car, 163 bhp version.
So first off the heater water valve had been connected with a direct vacuum from a T off the fuel vacuum line. He froze during the 4 hrs drive home!
So re attached the heater valve to the vacuum line that comes from the solenoid.
Now has some heat but there is no response to the temp dial. Its stuck on warm, not hot or cold now.
It does not move the flap motor or open the heater vacuum solenoid.
solenoid has vacuum on the input but never passes it to the heater valve. Could not pick up a voltage attempting to switch it the solenoid.

directional flaps are operating (feet, screen, full defrost) but the heat flap motor does not move when adjusting the temp dial.
​​​​
pulled the plug to that motor. Pin 4 and 5 on the plug has 10v. That does not alter if the temp dial is turned.

So I set the temp dial to low and applied 12v to pin 4/5 on the motor. The motor and arms fully extended.

Put the plug back in and the arms moved back in the opposite direction.

So it appears adjusting the temp dial is doing nothing to control either the motor on the left side or the heater valve solenoid on the right.

Any other checks I can do before pulling the control unit out?

Thanks Rob


Old 12-12-2023, 12:15 PM
  #35  
Donkeychobo
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As a side note, the vacuum line feeding the heating system input and res tank is coming off the fuel system and not the brake servo as others show.
The brake servo has no fitting for a second smaller vac line where its feed pipe connects, neither is there a T fitting on the servo pipe. No sign there ever was one, all looks original.
Did some cars come from the factory taking the heating vac supply from the fuel vac instead of from the servo?
​​​​I am getting 20 inch of vaccum on a gauge and it easily closes the heater valve if put directly on it so assume it has enough to not be affecting the heating control.
Old 12-12-2023, 01:25 PM
  #36  
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Further testing at the heater flap motor plug.
service manual says. Temp set to cold
Term 1 & 2 = 6v yes ok
Term 1 & 3 = 2.5v no, just getting milivots
Term 1 & 4 = 10v no, 0.1 v

Set temp to full
Term 1 & 4 = 0.1v yes
Term 1 & 5 = 10v yes
Set back to cold and should go from 10v to 0.1v no, no change

So unless another fault is causing this, it is looking like the control unit itself?
Old 12-13-2023, 12:38 PM
  #37  
Donkeychobo
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Not sure if anyone is reading this thread but here is another question. The car has climate control, or at least it has a climate temp **** with numbers not colours. I thought I'd check the sensors for resistance values but there is no pipe running to the dash temp round slotted opening and the under bonnet one (under the thin plastic cover over the fan unit) is not there either. So for non aircon but Climate control cars which sensors should be present?
Old 12-13-2023, 02:06 PM
  #38  
Donkeychobo
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OK, something is not adding up. Checked and there are no temp sensors fitted. Checked the build label in the boot and it lists no option codes for aircon or automatic heating. So the unknown is why does the car have the dash panel showing the temp control numbers as opposed to the blue/red lines. Has the panel being changed, has the CCU unit been changed ?
What is the difference between a basic control unit and a climate one?
To repcap, all heating controls work except. 1. The mixers flap motor does not move whatever the temp is set at. 2. The heater valve solenoid is getting no signal
Old 01-08-2024, 10:32 PM
  #39  
Steve Pratel
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Glad I found this thread and am reading through it.

I have been hard at work getting my newly acquired S2 up and running. Picked up the car in September, replaced the full fuel system, clutch and master cyls, all belts, hoses, water pump, cam chain, etc. Finally started the Car on Saturday, and all is well mechanically, now am sorting through electronic glitches.

Pics below are of my Climate Control unit. It went up in smoke back when I first acquired the car. I do not recall if any of the controls were activated, but when I turned on the key to close the windows and sunroof, I smelled something burning and smoke came from the Control Unit.

The Fan works, and the AC switch engages the cooling fans, but other than that the unit is dead (obviously). I have checked all fuses, and none are blown, and most importantly the AC compressor fuse is a 7.5. The car has NO evidence of mice, and was stored in a climate controlled and dry garage. Car has 44K miles, and other than a dead Tach, everything else electrical works without issue, and no warning lights.

My question is is it possible that the capacitor shorted and burned out? or do I have an unfused short somewhere in my climate control wires? I dont want to source a new part only to have it burn out immediately if I have a dead short or issue elsewhere.

First PICs are of the refreshed engine compartment. It runs as good as it looks. Very happy. The second two are of the Climate Control Unit. Thanks for the help.


Refreshed engine bay

Cleaned up Valve Cover with 0000 Steel wool and Mothers metal Polish, topped with Ceramic

Backside of Control unit

Looks like the capacitor shorted and fried.

Last edited by Steve Pratel; 01-08-2024 at 10:34 PM.
Old 01-09-2024, 04:15 AM
  #40  
Donkeychobo
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Steve,

You can test much of the system via the plugs that go into the control unit. It may help detect if anything else is not right.
​​​​Going into the controller from memory are,
Power.
Feedback positions pots attached to the flap motors.
Two motors
Two solenoids that open vacuum lines
3 temperature sensors

A list of tests can be found here.

https://********.com/viewtopic.php?t=357

The burnt out unit. I'd replace any components that look damaged, check the tracks etc. You can test some components with a decent digital meter. Look for any other electrolytic capacitors on the board. Those may bulge when failing with age and can be removed to test, values usually rise if starting to fail.

Next most common failures are regulators, transistors etc. Can be tested with the meter.
There are some ICs on the pcb which I gather are no longer available.
​​​
Failing this its a case of buying a used unit but some of those can be faulty so ask first. There are 3 models, non climate, climate, aircon.

Good luck.
Rob


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Steve Pratel (01-09-2024)
Old 01-09-2024, 04:19 AM
  #41  
Donkeychobo
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Sorry, site has removed the site name from the link. Maybe its not the done thing to mention it.

When you need help though you need help.
car pokes - all one word.
Old 01-09-2024, 07:20 PM
  #42  
Steve Pratel
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Originally Posted by Donkeychobo
Steve,

You can test much of the system via the plugs that go into the control unit. It may help detect if anything else is not right.
​​​​Going into the controller from memory are,
Power.
Feedback positions pots attached to the flap motors.
Two motors
Two solenoids that open vacuum lines
3 temperature sensors

A list of tests can be found here.

https://********.com/viewtopic.php?t=357

The burnt out unit. I'd replace any components that look damaged, check the tracks etc. You can test some components with a decent digital meter. Look for any other electrolytic capacitors on the board. Those may bulge when failing with age and can be removed to test, values usually rise if starting to fail.

Next most common failures are regulators, transistors etc. Can be tested with the meter.
There are some ICs on the pcb which I gather are no longer available.
​​​
Failing this its a case of buying a used unit but some of those can be faulty so ask first. There are 3 models, non climate, climate, aircon.

Good luck.
Rob
Rob, thanks. Is very helpful I found and bookmarked the thread with the schematics. I've attached them.

I'll test everything out, and will likely buy a new unit if everything tests out, which I think it will. Hate to spend the $$ but I am committed to a full and close to concours as possible, and want to enjoy the car without worry. I do want to check to see if the AC Compressor clutch is shorted. Theoretically that would have blown the 7.5 AMP fuse.
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Old 01-12-2024, 05:38 PM
  #43  
Steve Pratel
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Today I ran all the tables and tests from the file. All the motors worked as they should, and sounded fine. I also tested all the resistance of the sensors. Everything measured as expected with the exception of the 3 temperature sensors. They all read open, or how that will impact the system. I'm going to go back and check them again. I can easily access the outside temp which is on the blower intake.

I also pulled the plastic cover over the blower motor, and checked for any shorts or mice damage. No issues that I can see. I think the unit just failed and a capacitor crapped the bed. So the question is, do I drop significant coin on a used unit or new? I'm leaning new given how pristine the rest of the interior is.



Old 01-12-2024, 07:18 PM
  #44  
Donkeychobo
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Have you checked the temp sensors are fitted?

odd they read open. So you get no resistance at all?
Are you getting a good contact when checking.
They should read roughly 10k in average temperature.

​​They are critical to operation.

Old 01-12-2024, 07:32 PM
  #45  
Steve Pratel
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Originally Posted by Donkeychobo
Have you checked the temp sensors are fitted?

odd they read open. So you get no resistance at all?
Are you getting a good contact when checking.
They should read roughly 10k in average temperature.

​​They are critical to operation.
I'm going to double check to make sure I am measuring correctly. I can see the outside temp, where are the other two?


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