citychap26

Hi All,

I have an issue with my heater, normally the issue starts as follows, I drive to the supermarket, no issue (10 minutes drive), do my shopping then I notice that whilst driving home the heating comes on automatically on setting number one.

Points to note that the heater control unit works fairly normally in the I can select all 4 speed, however when turning the fan off, it does not turn off.

I think that this is also causing a drain on my battery. I have tried to look on google for an idiots guide solution, sorry if this has been discussed many times.

Thanks in advance.

Cheers

Sunil

ToreB

I am not sure what you mean by heating comes on automatically. The air temperature is adjustable with the temperature ****, and the fan speed is controlled by the fan speed ****.
If this is a 964, the fan speed is the same on speed setting 0 and 1, the first generation 964 Climate Control Units (CCU) does not allow for stopping the two main blowers. However, they shall stop at ignition off.
On the the later 964 units and all 993 models, the fans are adjustable from zero to full speed. What is the part number of your CCU?

Cheers,
Tore

citychap26

Hi,

thanks for the reply. So it would appear that hot air is blowing out from the screen vents, floor vents and also dash vents if I turn them on, and heater is not switched on. I hope that makes sense?

oh and it’s in my 993 C4.

Cheers

Sunil

ToreB

Great. I guess you have an inop mixer valve servo motor or two. They wear out, and will then stop in any position. Yours seem to be stopping while open, and this pours hot air into the ventilation system.
See this DIY guide on how to test the servo motors and fans: https://www.bergvillfx.com/categorie...test-procedure
Cheers,
Tore

pp000830

Hi Sunil,
The two servomotors Tore speaks of are in the footwells' outside walls of the car left and right. They are easy to remove only needing a Philips screwdriver to pull them out or back in.
They can be rebuilt oftentimes for a lot less than buying new.
Here is some additional info on the subject:
https://993servicerepair.blogspot.co...ning-hvac.html
The bottom of the page includes notes on rebuilding the mixing servos if you are going to consider doing it as a DIY Kitchen table project.
Andy

citychap26

Hi Andy and Tore,

Thanks for the llinks, I'll have a go at trying to "fix" the servo.I had a slightly hot journey from Croydon to Wimbledon on Sunday, to make matters worse I can only open the drives side window at the moment. I need to fix the passenger side.
Cheers

Sunil

pp000830

Hi Sunil,
Sometimes wiggling the other switch that controls the passenger window allows the driver-side switch to work they are linked together.
Andy ;-)

Foxman

I’m done with all the voodoo mixers and servos in my 964. I deleted the CCU and the entire HVAC suitcase (sorry Tore).

I don’t really need weighty AC here in New England. And with the help of a few Oatey 3” plastic test plugs, I can still have some heat when I need it.

Oatey 3” test plug

Manual heat

citychap26

Hey Andy,

switches work fine however I think the window has come off the runners, I need to take the door card off and see what’s broken.

Cheers

Sunil

95_993

Sunil,

It's likely your window lift rail has rusted out...pretty common.

Here's a good video on the replacement

https://m.youtube.com/watch?v=5gTgng3p3QM

Mike Murphy

I used to have a 3.2 Carrera, and the heat came from the exhaust manifold, driven in part by the engine air fan. If those valves aren’t shutting all the way, I’d get heat in the cabin, even if all blower motors and heater were turned off.

Does the 993 get heat in a similar fashion?

FredSmith

Hi, I've read through the threads on the problem of the 993 heater staying on, mine is doing the same so shall investigate the various servo's. Thanks to all for providing the info. But anyone had experience with the Heater Control unit (non air con) in the dashboard? For the last couple of years mine would work as expected but only when the gearbox was in neutral. For example, engine in neutral the heater **** blue to red operated perfectly, the fan speed 1 to 4 also perfect, but as soon as i put the car in gear the fan speed would drop to 1 regardless of whether the **** was positioned 2,3 or 4. It didn't affect the heating.
Now the heater is stuck on hot through all vents so I will need to investigate, but would be interested in any thoughts? Thank you.

ToreB

I guess you have multiple faults in the ventilation system, and several items have failed to render it completely inoperable at the end.
I would start with using an OBD diagnostic tool and read out any fault codes from the Climate Control Unit. Then, do a test of all the components, especially the servo motors and fans as explained here: https://www.bergvillfx.com/categorie...test-procedure
All the best,
Tore

Jonny Retrofit

There is a connection between reverse gear switch and the CCU - normally this closes the heat mix flaps. Could it be the reverse switch is broken? Check the reverse lights - are they on all the time when not in neutral?

ToreB

Johnyy, thank you for the correction, I have edited my post above. I agree, it could be an idea to check the reverse circuit, as well as the HVAC servos and fans. FredSmith, is your Climate Control Unit original to the car? Which part number is the unit, and which model year is the car?
Cheers,
Tore