Probs with adjusting Cab temperature

[Mr.FixitNorm]

Hi All,

posted this in the HVAC temp sensor post by alas no replies so I thought I'd try a seperate post !

My 944S doesn't have A/C but has the traditional blue to red temp dial, trouble is when I alter the dial the air coming out of the vents is either stone cold or volcano hot ! When I change the dial the transition from heat `on' or `off ' is precluded by a click from somewhere behind the dash and what sounds like a servo operating.

What I need to know is if there's any form of temperature thermostat that should be operating ? On other cars I've owned you adjust the cab temp by mixing air from the heater matrix with external cold air, usually by mechanical means, this doesn't seem to happen on my 944 and it's getting anoying having to constantly switch the heat on or off all the time.

I've checked the original Porsche PDF's and the Haynes manual but because they all show the A/C as well it's difficult to identify any sensors.

Any help would be most gratefull

Cheers,

Norm

 

[robwright]

OK after having shufty your system should be the same just minus the evaporator in the HVAC unit. You need to check for the following. In the right hand scuttle under the plastic cover at the blower inlet there should be (if your system is similar) a plug with a small thermistor in it. In the cabin there is what looks like a slotted vent by the fag lighter. This is the cabin sensor. Attached to the rear of this should be a flexi tube, which in turn fixes to a fan. This is the sniffer fan for cabin temperature. On the housing of the fan should be another sensor. The last is the mixing chamber sensor. If you remove the cover that fits over the centre heater grill (with the demistor sign at the top of the centre slider) tyou will see this sensor attached to a cable suspended in the output stream of the mixing chamber. The cocer aslo extends around the instrument binnacle. If you are careful you can remove it without removing the steering wheel.

 

[Mr.FixitNorm]

Cheers Rob, this sounds like a saturday morning job !! I guess the trick will be finding out whats happening ( or not! ) as the case may be. I have had the dash off to repair the hazard light switch last year, I wonder if I damaged or moved the sniffer tube in some way. If not I'll replace the thermisters as per the HVAC post.

We have a Farnell account at work so I should be able to get a good price on the parts.

Many thanks,

Norm

 

[944Turbo]

Having played with a red/blue set up about 12 years ago I dont think there are any temp sensors, I believe the later non AC cars with numbers do have them though. There are IIRC 2 servo motors on the left side beside the glovebox and also the valve under the bonnet for water flow. There are details in the workshop manual somewhere for what each servo does and also details to apply volts to move them manually. There are further servos on the right side of the heater but i think that is to do with where the air is directed. Thats as much as I can remember for now, one of mine had seized but it came apart cleaned up and worked fine from then on.
Tony

 

[robwright]

I just dug out the diagrams and they don't list air con or non air con either so I presume the electronics are the same. After all if my aircon is not switched on, which obviously it isn't at this tim of year and the fact it doesn't work at the moment then essentially they should be the same. Hope I am right mate.

 

[robwright]

In that case then the servo motor for the temp flap will just move by an amount determined by the temp knob. I.e it will not automatically adjust to suit temperature it will set an a value that you decide depending on knob setting all blue fully shut and all red fully ope). This may simplify things to either a defective knob, control unit, servo motor or the linkage between motor and temperature flap.

 

[Mr.FixitNorm]

Looks like the remedy may have got a bit simpler ! but still sounds like a saturday morning job.

Thanks guys, what a nice forum this is !, I really must get to meet some of you and your cars. The Rutland meet is a bit too far for me at the moment, I keep hoping I'll see someone locally though ( a few months back there was a nice `H' reg silver S2 parked near the shop where I work but I didn't see the owner before it went.)

Regards,

Norm

ps can anyone put a legend to each of the message smilies, I can't make out what some of them are suppose to represent ? On another forum I go on, if you hover the pointer over a smilie it comes up with what it represents ie frown / grin / smile etc

 

[pauljmcnulty]

ps can anyone put a legend to each of the message smilies, I can't make out what some of them are suppose to represent ? On another forum I go on, if you hover the pointer over a smilie it comes up with what it represents ie frown / grin / smile etc

We just use them at random. []

[] happy
[] laughing
[8D] oh yes!
[] wink
[&:] confused
[] angry
[] crying
[:'(] feel sick
[] oh no!
[:-] poke tongue at you
[8|] hmm, that's an idea
[&o] sad.


[>:] and [X(], I don't know? [&:]

 

[zcacogp]

Norm,

As already said; as I understand it, the 944's with just the red/blue stripe simply have a direct connection between the temperature dial and the mixer flap servo. They don't have the temperature monitoring and correction system that the ones with numbers on the dials have. Therefore, if you are having a problem then have a look at the servo and the wiring going to and from it, paying particular attention to whether the servo moves when the dial is moved.

Given that the dial is a rheostat, it is possible that this has failed such that it is not offering a variable resistance correctly. If this is the case then swapping it would be quite a simple fix, but you need to do some investigating to find out whether this is the case.

As far as smilies goes, these threads may help.

http://www.porscheclubgbforum.com/tm.asp?m=358121&mpage=1&key=smilies&#358551

http://www.porscheclubgbforum.com/tm.asp?m=535653&mpage=1&key=smiley&#535653

[]


Oli.

 

[Diver944]

ORIGINAL: pauljmcnulty

[:-]    poke tongue at you

Is that a tongue???? Damnit, I always thought it was a finger being held to the lips as if to indicate 'Sssshhh'

Now I need to go back and edit all my smiley sssshhh posts []

 

[zcacogp]

Mr Smith in "Mods Don't Understand Smilies" shocka!



(Keeping it on topic, I presume this is the correct smiley for "My heating is jammed on 'Alpine Winter' setting and the gearknob in in danger of melting: [] )


Oli.

 

[Mr.FixitNorm]

Just a quick update, I stripped the dash front off yesterday and tried to observe what was happening when the various heating controls were operated. The red / blue dial as stated controls nothing more than a mixer flap behind and just below the centre vents. The flap moves over the full amount of travel when the dialis operated BUT, it does so with only about a third of a turn of the dial, i.e. the flap is on the full heat setting when the dial is only just into the `red' setting. This suggests that maybe the rheostat is faulty as I would have thought it should only be fully open when the dial is on the maximum red setting !

The other thing I did was to remove the cover over the fan setup under the bonnet. This revealed what I think is a resistor on top of the fan housing, ( picture 1 ) it's only a guess as the wiring diags are a bit confusing but I think the resistor must be to do with the fan speeds - somebody will either confirm or correct me on this !

The other two pictures are what appear to be air pressure or vacuum operated solonoids which control a flap at each end of the fan housing to presumably reduce the external air intake. I assumed the air recirculating switch on the dash would operate these to close off the external air intake, when I tried this nothing happened so I'm still not sure if the recirculating switch is working or these flaps are for something else ?

ATB

Norm

 

[robwright]

Norm in your second pic that plug that is cable tied down should have an external temp sensor fitted in the end of it if I am not mistaken. It looks just the same as the climate control one. Yours appears to be missing!! It has then been cable tied in place because the missing sensor attaches to the bracket. To remove the sensor is a common quick fix for climate control option. The sensors go open circuit making the CCU think the outside temp is like the sun. By removing the sensor you make it open circuit and the CCU thinks it is minus a million outside. As opposed to nothing happening with temp till about 27 when the sensor is short circuit it kicks in very early at about 18 when it is open circuit.

 

[944Turbo]

should an F reg have a numbered dial? has someone replaced it with a blue/red one and removed some sensors I wonder? Or does a red blue dialed car still monitor incoming air temp - anyone got one they can check?

The vacuum valves also control the valve for the coolant. Its in the engine bay at the back of the head.
Tony

 

[pauljmcnulty]

This revealed what I think is a resistor on top of the fan housing, ( picture 1 ) it's only a guess as the wiring diags are a bit confusing but I think the resistor must be to do with the fan speeds - somebody will either confirm or correct me on this !

Indeed. This resistor controls the fan speeds, if it fails you only get off or speed no. 4.

 

[Mr.FixitNorm]

Rob, I don't think mine had climate control as the the red/blue dial only controls the flap behind the centre vents, I would have thought that there would need to be some major rewiring if the climate control type system had been removed. I've had cars in the past where part of the wiring for higher spec versions is included as it's part of the loom, not sure if this is the case with mine but I would have though if the climate control sensor failed it would have been cheaper and easier to replace it rather than fit a new internal dial and wire it up to the mixer flap direct !

Tony, those vacuum operated valves seem to do nothing more than operate a flap on each end of the fresh air intake ( I can move the connecting rods by hand and close / open the flaps, but nothing I do with the heater / fresh air controls makes them operate??

Does anyone know if there is a data base or way of finding out what spec the car left the factory in ??? I'm wondering if Porsche themselves would have records going back that far and/or would be willing to check?

If anyone out there has a 1988 944S it would be nice to know whats fitted to it, although I guess when it was new the original owner could have spec'd what ever he wanted. - anyone know how much my car would have been new?

Thanks,

Norm

ps - thanks for the confirmation Paul !

 

[robwright]

It doesn't look as if it has been professionally done though does it? I think the flaps are purely for recirc air as you said. The heater control valve is located at the back of the block. Both the recirc and heater control valve are controlled by a couple of control solenoids on the right hand side of the HVAC unit under the dash.

 

[235tonyw]

Hi Norm,

I had a similar problem on my S2 cab when I got it - perminatly on hot?
Not sure if S heater the same? If you remove the glove box (screws at sides take door off 1st) on right of GB (RHD car) area you will see a lever rod held by small plastic part that runs in a rail slot that rotates when temperature dial is turned. The rod is attached to a letterbox type flap at opposite end that controls the hot air inlet from heater. On mine the plastic part which hooks through rail & holds the rod in between 2 serrated fingers had broken 1 side & rod became detached, leaving flap wide open = max heat?
Most experianced parts staff at local PC will know part concened about £1 each. Yours may not be broken but if the rod is not located correctly in plastic grip ie full temp on dial, flap held wide open then clip in place = correct travel from hot to cold! The end of the rod link is like that of the metal hook on a plastic coat hanger sort of ribbed not a thread which holds in the plastic clip - if it slips or is not clipped in correctly you get a limited & incorrect temperature range? Hope this helps?

 

[Mr.FixitNorm]

Cheers for the info Tony, The dial does move the flap but as you say, incorrect fixing may be the cause of reduced sensitivity. I'll check that at the weekend.

I also spotted your post on the belts change in this area, I might give that chap Sean at two counties garage a call as my cam belt should probably be changed ( Last done by a Porsche specialist 10,000miles ago but also 6 years ago !! )
I must admit whilst I know that many on this forum have way more knowledge of 944's than me, most cars I've owned in the past that have cam belts have always specified changing on or before set mileages rather than time intervals. Given the high quality of Porsche engines and craftsmanship, why do the belts need changing at such short time intervals?

Regards,

Norm

 

[pauljmcnulty]

I also spotted your post on the belts change in this area, I might give that chap Sean at two counties garage a call as my cam belt should probably be changed ( Last done by a Porsche specialist 10,000miles ago but also 6 years ago !! )
I must admit whilst I know that many on this forum have way more knowledge of 944's than me, most cars I've owned in the past that have cam belts have always specified changing on or before set mileages rather than time intervals. Given the high quality of Porsche engines and craftsmanship, why do the belts need changing at such short time intervals?

At the risk of sounding like a doom-monger, I'd not turn the key in a 944 with belts over four years old. Just get it done, there's no more heartbreaking post on here than someone who's engine has been lunched by a broken belt and it's often the end of the car. There have been a small number of failures pretty soon after the four year limit, but as not many owners would contemplate letting it go any longer than recommended, I'd think it's quite a significant percentage of the cars with very old belts on that fail.

Belts do degrade over time: other car makers might have different intervals but then they might have a different type of belt. You don't know how old the belt actually is, either; people here have pointed out that it could have been on the shelf for years before being put on the car if the garage or supplier doesn't see many 944s.

Also, if the belt has been contaminated it will degrade faster. My first belt change lasted a whole two years, as the seals were worn and allowing oil to mist out over the belt. I'm sure someone will come up with a story of a 944 with belts that are a thousand years old and still going, but to me it's just not worth the risk.