Porsche Enthusiasts Club Forum

I set to the car with the Mityvac this afternoon. Symptoms were no air to the footwells, aircon to screen only, very slow response to heater controls and only hot air available for the first minute after restarting.

First thing I checked was the fault.....the vacuum check valve was hardly working, as if it was blocked. Massive difference in heater/aircon operation now. Something easy and cheap for a change!
While I was at it I removed the centre console and replaced the window switches, plus the temperature sensor unit which was broken.

That's fantastic Lightning - glad the MityVac proved handy.

Did you have a spare blue/black check valve?

I also have console out now and am fixing similar fault. The fan motor for the temp sensor is only moving sluggishly and isn't really fixable unless you can retrieve the shower of brushes and springs which emerge when you open it up! I am picking up new fan tomorrow (looks like a miniature of the Teletubbies Noo-Noo) from Porsche Solihull who kindly flew one over from Stuttgart last night.

How did you test your temp sensor and where did you source replacement?

Hi there,

My fan was OK. I replaced the sensor as the outer part was broken, it cost £60 (!) from Porsche. It may have still been working. How much is the fan unit?
The valve I sprayed WD 40 into it and blew it through and it cleared. I've ordered a new one from Porsche, it's £10.

I couldn't get the console completely out, I removed all sorts of wires but it still would not release. However I managed to get it a couple of inches away from the dash and this was enough to do the work.

The fan unit was painful. Porsche doubled price of it 6 months ago apparently, so is £140 though I only need the motor which looks less beefy than one in a Scalextric car. The motor can't just be replaced by any 12V the right size as it's a super quiet design. Have tried to contact original manufacturer about it (Johnson) but no joy. Oh well should last another 20 years.

I recently sold on eBay the blue/black valve. Perfect condition and went for princely sum of £1. Only changed it as preventive maintenance. I obtained one with a load of other bits from US and it's $15 there so same price here.

There are some well hidden screws holding console in:

- at 'top' end 2 screws on underside of glovebox
- similarly 2 screws on the other side
- but most hidden is inside glovebox, pop off rubber blanking grommet to reveal hex head screw

Did you pop out the tabs at base of transmission handle?

You did well to manipulate the temp sensor out with only a few inches to play with.

With sides of console off it's very easy to check the external temperature sensor too which saves you going in via wheel liner or headlight to examine it. The external sensor is a favourite to fail - either the thermistor or just as likely a dislodged or corroded connector where it's mounted at end of alternator cooling hose. If you need more details just shout but it's a simple resistance measurement. If the ext sensor is open circuit then it renders your new internal sensor useless as they are in series!

If you're curious about original cabin sensor just put ohmmeter across the two yellow wires. It will measure about 4K ohm, and if it's working ok the reading will drop by a few hundred ohms when you blow on it.

While you're in there it's not much more work to check all the vacuum actuators if you haven't already done that, as well as the vacuum solenoids. I was pleased and frankly surprised to find none of mine were leaking.

I put the Mityvac on at the check valve and set to pumping it up, therefore testing the whole system at once. After a while I achieved a vacuum, which held fairly well. After I fixed the check valve the various valves worked so well (compared to before where they hardly worked at all) that I just put it all back together and closed the garage door on it.
Total time on the job was five hours.

I did get all the screws out, it took a while to find them all as you say, but did not remove all the wires, and could not work out how to remove the gear shift parts. But I got the job done, so all ended well.

Can't the motor be repaired? It'll probably only be the carbon brushes worn out. Can it be dismantled? I'm used to vintage cars and also vintage television/electronics etc where almost everything has to be dismantled and repaired.

Did you turn ignition on and operate hvac controls during the test?

Went to pick up sensor fan today from OPC Solihull. They were mortified when I opened sealed box (correct p/n sticker) to reveal completely wrong bit from a 944!

Will delay me for a few more days now till another flown from Germany.

I'm sure motor could be repaired had I trained as a watchmaker! Very diddly, and I'm very used to electronic circuitry. I wimped out

Yes I can see that, plus it's not something you'd want to have to take out again if the "repair" failed!

I did not operate the heater during vacuum testing, but did check a couple of the valves. Water valve and footwell valve (which was not working). After I got it working I'd been on the job over four hours and still had it all to reassemble, including the air filter housing in the engine bay, so I called it a day at that.

Also I noticed that the driver's door window seemed a bit loose, it goes up and down OK but if you hold the glass you can rock it about an inch about the centre. So the next job is to dismantle the door before it gets worse and see what's wrong there.

Got a pic of the motor? Johnson make model motors so wearing my model makers hat I may be able to help.

Hmm, problem is that without energizing solenoids you can't tell if the leak or any of the actuators to which they route vacuum. You need to pump vac with power off, then turn on and see if vac holds, then operate vent slider in all positions to see if it holds (will drop slightly as some actuators are fed vacuum).

Thanks for offer Jim.

The number inked on case is 1 397 220 163 (12V). Looks slightly battered in the photo where I pried tab to open it up.

Diameter 27.05mm, length 31.73mm, shaft 1.75mm

I've looked on Johnson's website and they still make motors specifically for hvac systems, but none of those match this one. I understand the design is extremely quiet (you can't actually hear the motor unless you have complete silence - usual test for it working is to hold a lit ciggy by it but that's no use to me as non-smoker! I think I checked some of their model motors too but none had the precise same dimensions. In fact before I found the design was super-quiet I was going to check in my local model shop too. Have emailed the UK Johnson office which is in fact very near me (Coventry) but not heard back yet. Not surprised as they can probably guess I'm not about to place order for 500,000 hvac motors!

A guy on the 928 owner's list had a used one for me from car he's breaking, but at last moment discovered the one in his 928S wasn't working either! He wanted to stick to his word but I wouldn't hear of his sending it to me when he needed it.

Should be obvious when you remove door cards, but probably either the felt covered anti-rattle bumpers just where window enters door, or the vertical window guide which the window rides up and down. It can come loose from its fixing at the bootom.