Heater problems on UK spec 1985 carrera.

[ant7]

hi all,
i wonder if some of you guru's can help, i have recently purchased a 1985 carrera, now amongst the many issues that needed sorted, the heater system dosent work, the electronic valve between the seats functions and i have removed its side panel to check the movement of the rod gear etc.
i have also removed and checked the relay in the engine compartment for obvious signs of broken circuit board tracks, both relay coil continuity etc, both the hot air fan and cold air fan are working when the relays inside the main relay are pushed manualy , however, no matter what i do with the heater controls nothing works, this car had air con originaly but the pump has been removed, would this affect things ?
please i would appreciate all input on this as i realy need to get things working before the winter!
Anthony.

[Oh Haha]

If the red lever moves up when you turn the dial on the heater console then it is working........to a degree.


What you need to check is if the flappers under the car are closing when you call for heat. If they are stuck open your heat is going to the outside world.

Jack the car up and safely put it on stands. Crawl under the car and loook at the back of the exhaust headers. There should be fexible hose that connects to the headers. Follow it "up" and you'll see the flapper boxes along with the cable that is attched to the control unit between the seats.

Check this out and report back with your findings. I'm not an expert but this is a common problem and we'll do everything we can to get you assistance.

[Drisump]

I don't think he has levers Oh Haha, I think he has the auto type. That is, there's only a dial between the seats and no levers. To ant7:can't help you, trying to solve my own similar problem....I don't drive my car in winter so it's kind low priority. Cheers

[Hugh R]

Besides checking the movement of the rod on the servo, did you check that both end sockets are connected to their respective balls? Mine had popped off of the rear one, I reattached it and put a plastic wire tie on it to secure it.

[Oh Haha]

The autoheat has a red lever that moves on a servo connected to the flapper boxes.

[ant7]

hi all,
thanks for the replies so far, I havent got the older SC type heater system, mine is the auto type,[no red levers etc] I have been under the car and checked the flappers are free, there is heat, i just cant control it, ie; no fans, no matter what position i put the dash controls on, As stated, I have checked the operational state of both motors, and they are working.
I have since read the trouble shooting guide about the relay fix, which may cure some of the issues,However, i could use some more thoughts on this please.
I will only be using it on dry fine days in the cold!
Anthony.

[SilverWT]

Originally Posted by ant7

hi all,
there is heat, i just cant control it, ie; no fans, no matter what position i put the dash controls on,Anthony.

Hi Anthony,

The controls on the dash do not operate the engine or footwell blowers. The only input they have on the heating is the direction of the flow (footwell/dash) and the mix with fresh air. Both engine and footwell blowers are controlled by the dial on top of the autoheat. Their operation depends on the setting you put on the autoheat and the temperature picked up by the temp sensor, except for the defrost setting on the dial which should turn them all on regardless of temperature.

Mark

[ant7]

Originally Posted by SilverWT

Hi Anthony,

The controls on the dash do not operate the engine or footwell blowers. The only input they have on the heating is the direction of the flow (footwell/dash) and the mix with fresh air. Both engine and footwell blowers are controlled by the dial on top of the autoheat. Their operation depends on the setting you put on the autoheat and the temperature picked up by the temp sensor, except for the defrost setting on the dial which should turn them all on regardless of temperature.

Mark

hi Mark,
thanks very much for explaining things, that now makes sense of things.
the cold air blower dosent seem to work, so i guess i will be getting that out and either reparing it, or replacing it, i have done this on one of my previous 911's.
The engine compartment fan works when i apply 12v direct, however, i am not sure about both footwell blowers, so i will have to do some more investigating.
I am quite sure some of the issues are caused by the reed switch in the relay [engine compartment] but may have to examine the heater control unit again, just to make sure the rods are connected at both ends!
Thanks again.
Anthony.

[SilverWT]

The reed switch in the relay controls the footwell blowers, not the engine bay blower. It detects the load from a running engine bay blower so it does not switch the footwell blowers on when the engine blower is not on (or failed). This is why when you do a heater backdate (eliminating the engine bay blower to clean things up and reduce rear end weight, plenty of info on this is you do a search) you have to bridge the read switch in the relay to get the footwell blowers to work in the absence of the engine blower.

Are you getting any heat into the car? Even if no blowers are working the engine fan will move hot air into the car if the flapper valves are working.

Mark

[aj88cab]

From your description (fan motors not running) you might have a bad control relay module (silver relay box at relay panel in engine comparment that you refer to above) or a bad switch at the control console, or bad conductors from the switch to the control module. You mention you have power to the motors when you manually close the relays, so the issue is the contacts are not closing.

Check to see if the switch at the control console may be bad. This switch operates the engine blower relay. To check if you are getting power from that switch, remove and unplug the relay module and check pin #9 for power with the heater system ON (ingition in ON position or engine running).

If you are getting power to Pin #9, the issue is the relay module itself. If no power to Pin #9 then you will have to remove the control console cover and service the switch, or possibly the conductors from the switch to Pin#9.

[ant7]

Originally Posted by SilverWT

The reed switch in the relay controls the footwell blowers, not the engine bay blower. It detects the load from a running engine bay blower so it does not switch the footwell blowers on when the engine blower is not on (or failed). This is why when you do a heater backdate (eliminating the engine bay blower to clean things up and reduce rear end weight, plenty of info on this is you do a search) you have to bridge the read switch in the relay to get the footwell blowers to work in the absence of the engine blower.

Are you getting any heat into the car? Even if no blowers are working the engine fan will move hot air into the car if the flapper valves are working.

Mark

Hi Mark,
thanks again, and understood.
Anthony.

[ant7]

Originally Posted by aj88cab

From your description (fan motors not running) you might have a bad control relay module (silver relay box at relay panel in engine comparment that you refer to above) or a bad switch at the control console, or bad conductors from the switch to the control module. You mention you have power to the motors when you manually close the relays, so the issue is the contacts are not closing.

Check to see if the switch at the control console may be bad. This switch operates the engine blower relay. To check if you are getting power from that switch, remove and unplug the relay module and check pin #9 for power with the heater system ON (ingition in ON position or engine running).

If you are getting power to Pin #9, the issue is the relay module itself. If no power to Pin #9 then you will have to remove the control console cover and service the switch, or possibly the conductors from the switch to Pin#9.

hi Andrew,
many thanks,
thats the kind of info i am missing, i needed to know what actualy activates the relay coils to switch them as i have power to the fan motors [well the engine bay fan and at least one of the footwell motors] when i manualy push the relay contacts together [cover left off relay to do this] so, it would seem that the initial issue i have mainly relates to the control unit switching.
So,onto my next question, Is it easier to remove the whole control unit and examine it out of the car, or am i better off removing one of the seats and pulling off the side cover to investigate ?
Realy appreciate all the help i have been given on this by you guys so far.
Anthony.

[aj88cab]

Anthony,
You will have to remove the console cover to get to the switch and conductors. You will not really be able to service things thru the side access panel. I have removed the console cover with the seats in place using an extension, its getting the screws back in that can be frustrating, but it can be done. Much easier if the seats are out however.

[ant7]

Originally Posted by aj88cab

Anthony,
You will have to remove the console cover to get to the switch and conductors. You will not really be able to service things thru the side access panel. I have removed the console cover with the seats in place using an extension, its getting the screws back in that can be frustrating, but it can be done. Much easier if the seats are out however.

Hi Andrew,
ok, understood, thanks, i will let you "All" know how i get on.
Anthony.

[Peter Bat]

There are a couple of other things that can stop the auto heat working. The cabin temp. sensor can go open circuit. This has happened to my targa, a sod as the cable is threaded around the windscreen and can't be replaced without taking the windscreen out. There are also 2 interlocks to stop the engine comp. fan when the engine is cold and when the car is stationary. A temp switch connected to pin 10 (relay) closes when the engine gets warm. If this fails O?C then no fans. Pin A on the speedo goes to Pin 1 on the relay. If the car is not moving then Pin A is not active and again, no fans. Not sure what this signal looks like so I can't give any fault finding info. If anyone has any info that would be great.

[wazzz]

Signal from Pin A is basically a square pulse almost identical to speedo input signal received from ECU.

Both are of same frequency, but different duty cycle, since pulses are output with a fixed width whatever the frequency. Can't remember what their width (or duration) is.
This signal is then processed inside the heater relay to allow the overheat function to operate in case engine gets too warm (info is received on Pin 10 and provided by temp sensor on engine block closing to ground).
Overheat function is allowed to work only at lower speeds, including when car is stopped. Don't know what the threshold speed is, but it must be quite low.
Once car is moving fast enough, overheat function is disabled, probably because it is considered inefficient compared to moving air in the engine compartment.

Here is a diagram of the functional logic of this heater system that I traced and created some time ago. It is not complete. The "digital" part that processes the speedo signal is not shown (some connections and components were too uncertain to be shown).

Link to diagram

[Peter Bat]

Many thanks for that little bit of info about the speedo output. In the words of Michael Caine "Not a lot of people know that.
I am debugging my auto heat system at this moment and this little nugget will help in eliminating items.

[sus911]

Originally Posted by Peter Bat

Many thanks for that little bit of info about the speedo output. In the words of Michael Caine "Not a lot of people know that.
I am debugging my auto heat system at this moment and this little nugget will help in eliminating items.

Hi Peter. Did you ever succeed getting your footwell blowers to work?