Heater Update

[robwright]

I recently posted that my heater was struggling a bit with the cold weather, which I put down to old thermostats. I have a symptom update. If I turn on defrost then the heater will go to nuclear hot. This may suggest outside temp sensor yes? I was driving along A1 today and heater was being average (not freezing but not roasting). Decided to test my cold weather boost and gave it some beans. Hey presto heater was nuclear again, where it stayed until I pulled off the A1 and slowed down when it reverted back to usual. Also when I go to defrost I get lovely roasting air out of my centre vents but not normally. The same happened when the thing kicked back in on the A1 lovely hot air out of the centre vents - then not. As water pressure is obviously linked to engine revs should I be thinking of airlocks in the system or is as I originally thought my heater cursed by voodo magic []

 

[Riverside]

There are three thermistors, one measures intake temperature (under the bonnet on the offside hvac intake), one measures the cabin temp (at the end of the rubber hose leading from the small vent next to the cigar lighter), and one to measure output temp from the heater (just behind the centre face vents).

I had the exact same symptoms when I first got my car, replaced the output temp thermistor (circa £75 from OPC, £25 s/h from PH Sportscars or 4p from local electrical hardware store).

Follow the diagnostic list for the HVAC system (section 87), you'll need a multimeter, to find the faulty component & replace it.

 

[sulzeruk]

Rob, give the thermistor that is connected to the rubber tube a good clean as these always seem to get coated in fluff. The black one I am working on at the moment had a crimped pipe due to some cretin catching it when they had been putting the glove box back in! I have plenty good working spares if you need anything. Would also check for airlocks again if the temp is varying with right foot action.
Alasdair

 

[944Turbo]

Might also be worth checking the one way vacuum valve hiding somewhere near the back of the head its usually blue and black - if it fails boost may do strange things to the heater system,
Tony

 

[robwright]

Actually I was going to ask about the check valve. On all the diagrams I have seen on Lynsey it shows the valve connected to the brake servo or brake booster as it is known. This however is not the case on my car and as far as I know the brake servo has only one connection directly from the manifold. My check valve is however in the line that feeds the heater components and vacuum resevoir. Again vacuun resevoir. What's that for???

 

[944Turbo]

I think the American setup is a little different - they have the combined brake / clutch master cylinder> cant remember exactly how it is run but it should only allow airflow in one direction. I think vacuum reservoir is a store for when engine isn't running, probably also helps when you are on boost rather than vac.

Cant recall if when you pull the vacuum pipe off after the car has been shut down the vacuum is there, if it is there normally it might give you a clue if yours doesn't have it. My car is too far away to nip out and check - its hiding in the garage at my Mums.
Tony

 

[robwright]

OK spent a good day working on the car today - very fruitful. Most of it was spent diagnosing the HVAC system. These were my findings. The vent on the dash is supposed to have a pipe connecting it to the cabin temp sensor with the sniffer fan attached to it. Mine didn't have one. It had a tube connected to it that snaked it's way all the way over to the other side of the HVAC unit and connected to nothing???? As it was connected to nothing I used some of it to replumb the interior sensor to the vent. I also need an outside temp sensor. Mine was reading around 10 ohms and should be reading in the tens of KOhms. Practically a dead short as the manual suggested. Now where do I get one of them??? I also rebled the cooling system. Other jobs done today were:- Fiteed new servo motor to footwell flaps - now working fine. Fitted new motor assembly to drivers miorror. Many thanks to Alisdair for the parts. I also swapped the seat backs. About 40 minutes work and really easy to do. very chuffed with the results [][][] Sadly I ran out of day before I could tackle the headlight washer pump. Not too upset about that though. Very good days work can't think of a better way to spend Xmas Eve. Merry Christmas to you all. Even Scotty.

 

[sulzeruk]

I have a couple of sensors here Rob, will check them with a meter and chuck one in the post to you Monday. The turbo I am working on at the moment has a tube connected to the back of the glovebox. It is like a mini 911 heater hose with the brown insulation round it. Havn't traced where it goes yet but will have a look. Do you need one of the rubber hoses to connect the inlet to the motor Rob as well?
Alasdair

 

[Riverside]

The long winding tube could be the one intended to supply conditioned air to the glovebox, clearly not essential []

If only the outside sensor is faulty (shorting) try simply unplugging it. the HVAC system will then think the incoming air is very cold & should give you relatively normal operation until you can get hold of a replacement.

 

[robwright]

I think you are spot on there. There was a hole in the side oif the HVAC unit that I thought it may fit into but didn't see the point. I think I will now tape over the hole. What a useless item lol. Good tip about the sensor I think I will do that - essentially make it open circuit i.e. very very cold. Alisdair are you a drinking man cos there may well be a bottle of nice malt in the post to you mate. Two if you manage to get those sun visor clips and the passenger door handle []

 

[sulzeruk]

Hi Rob, I found the door handle today raking through stuff inthe garage whislt it was minus 10! I also have the clips as well here. I have a proper bung for the glovebox too if you want it Rob, came out the new S2 for breaking.
Alasdair

 

[robwright]

Yeah been pretty parky too here mate although not quite up to your standards. Nearly lost the old girl last night. Don't know if you read my post. So what's your tipple then mate? A single malt?

 

[robwright]

Captains log stardate day after Boxing Day. Removed the outside temp sensor and the heater is now turbo powered and controllable [] In fact very turbo powered!!! Bleeding the cooling system again had quite a dramatic effect also. In fact it improved cooling so much that the car is now taking 15 - 20 mins to get up to normal temperature in this weather. Definately thermostats in the new year I think.