How to repair heater control valve on a Porsche 944 (Square Dash Model)

THE WHY?

One of the good things about the 944 is that it doesn't take long for the engine to warm up, which is great in the winter when you need to de-mist the inside of the windscreen and heat the passenger compartment. However it's not so good in the summer if like mine your heater is always giving out hot air even when the heater slider is set as far over to the left handside (the cold setting) as possible. This is caused by usually one of two possible problems. Either the hot/cold slider has a broken cable or the heater control valve (HCV) is faulty. It is usually the heater control valve (HCV).

THE TASK

It is important to note here that the HCV and heater mechanism are completely different on the square dash 944 model to the oval dash 944 model. Oval dash owners should look here and here as this guide is only for square dash owners.

This job is relatively simple (if a little fiddly) and should only take an hour or two.

You will need the following:

Long & small flat bladed screwdrivers
Long-nose pliers
Heater Control Valve (approx £20 from Porsche main dealer)

THE HOW TO

(Amateur mechanic Job Time approx: 1-2 hours)

Firstly it's important to know what the HCV actually does. The HCV is basically a tap that allows hot water from the engine to enter the heater matrix. When you set your heater to hot the tap opens and lets hot water into the matrix and when you set it to cold the tap closes stops the hot water entering the heater matrix.

It's also important to understand how the heater controls work on a square dash 944 as I've seen alot of confusion over this on some forums. There are 4 controls for the heater. This is what they do:

Upper left slider controls the direction of heat (footwell & centre)
Upper right slider controls the direction of heat (centre & windscreen)
Lower slider controls the hot or cold setting
Dial to the left of the sliders controls the fan speed (Off & speeds 1,2,3)


To begin with it's important to make sure the cable that goes from the hot/cold slider to the HCV is not the fault. Start with the lower hot/cold slider all the way over to the cold setting as shown below.


Now open the bonnet and locate the heater control valve which sits tucked down at the back of the engine smack bang in the centre. Below is a picture of the heater control valve.


Because the heater slider is set to cold the heater control valve should have its white arm all the way over to the left hand side (as shown below). You can even see the cable extended.


Now go back inside the car and move the hot/cold slider all the way towards the hot setting. Go back and look at the HCV and you will now see the white arm has moved all the way over to the right (as shown below).


If the white arm of the HCV is not moving then your problem is with the cable. Either the cable has become disconnected at the HCV end or at the hot/cold slider end. Or the cable has broken in the middle somewhere. If the arm is moving you now know that it is very likely that the HCV is the fault.

To remove the HCV you will first need to remove a small metal clip that locks the black outer of cable to the HCV. Do this with your fingers or a pair of long nose pliers. DO NOT LOSE THE CLIP otherwise the cable will not be able to work the HCV. Now unhook the inner cable from the small hole at the end of the white arm on the HCV. Next you will need to undo the 2 hose clips that help secure the 2 hoses to either side of the HCV. Once this is done twist and wriggle the HCV loose from the hoses. Do not be alarmed if water comes out of either hose whilst doing this, just make sure you don't allow the lower of the two hoses to hang down once you have removed the HCV as water will go all over your clutch, just wedge it so that it's upright.

Below is an image of my new HCV (left) against the old HCV (right). Note the washer in the middle that appears to have come loose inside in the old HCV.


You are now ready to install your new HCV. Installation is the reverse of removal. By far the hardest and most important part is re-attaching the metal clip around the black outer of the cable, it took me several attempts and you might be advised to familiarise yourself with how the clip works with the HCV before you attach the hoses to the new one.

One last important thing is that you may or may not have to top up your coolant level as some will be lost when you removed the HCV.