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No hot air

N

noneil

New member
This problem started a couple of weeks ago, with the heat droppping off without any adjustments being made to the dial, in the end warm air would only come out when going about 70mph - which I wasn't very often with snow on the ground.

I've tried taking the external temp sensor off as suggested in other posts, but this has made no difference - just lots of lovely cold air.

I have noticed that the gubbins (that's not a technical term) behind the glove box seems pretty seized; I undid my 'repair' to the broken clip (from when it was only blowing hot air in the summer) and the arm that sits in the clip moves freely enough (not that it makes any difference, although I can hear a change) but the mechanism where the clip is mounted is solid.

Help!

Cheers,

Neil
 
Neil, there is a vacuum operated valve that controls the flow of hot water to the heater. You will probably find that that has stuck in the one position. The mechanism (one of three) only controls the direction of the air into the car via flaps. The heat is controlled by the vac operated valve. You may find that your control unit has given up the ghost (not at all uncommon!). Where in the country are you as there may be a technically minded member near to you who could have a look at the car for you.
Alasdair

 
Hi Alasdair. I'm in Leicester, but I'm pretty happy to have a bash at repairs myself if I know what I'm supposed to be doing - learning by doing, etc! It sounds like something is going to need to be replaced; can the valve be operated manually in the meantime?

Cheers,

Neil
 
Neil

the valve that Alasdair refers to sits at the back of the head right up against the bulkhead - between the bulkhead and the cylinder head just above the hall sensors. With the vacuum pipe removed you should be able to move the arm freely and as per your question, hopefully be able to rig up a cable to operate this from inside the car !
 
Depends on the model on an S2 the heater control valve is against the cam cover just behind the distributor and I believe is designed to fail hot so if you remove the vac line assuming it is working the valve should fail open and let hot water into the system, easy to check the valve operates with a syringe and piece of rubber tube, just disconnect the vac line and suck with the syringe, also easy to check if vac line is leaking by sticking a wet finger over the end.
 
Thanks for the suggestions guys - unfortunately I don't have an S2, but an 89 lux.

I didn't disconnect the vacuum (didn't want to break it - do I just pull it out or what?) but once the engine was warm I operated it manually and could feel no hot air from the vents; it always returns to the 'auf' position, and the pipe after it was warm to the touch (this of course could be just from the heat of the engine bay rather than the coolant in the pipe though). I guess the problem is further down the system.

I feel like the seized box behind the glove box has something to do with it. I've disconnected the flap-rods (that go upwards: one that clips into the breakale plastic clip; the other is clamped in with a brass nut) and tried operating them both manually and it makes no difference although I can hear a change when the flaps move.

What lies between that box and the vacuum?

It's gloves and scarves tonight for the drive to Birmingham!

Cheers,

Neil
 
If operating the control valve manually did not get heat into the system then the valve itself may be broken inside and not connected to the linkage you could try removing the valve and joining the hoses with a short piece of tube as a temporary fix at least it would get hot water to the heater matrix, alternatively you may have a blockage in the lines to or from the heater or indeed the matrix may be choked.
 
Neil, I have a spare valve you can have for the postage that I know is good. It is not hard to change on the car and the valves are the same over all the models. The vacuum line just pulls out. Is your coolant coming up to temperature as well? Could be the age old problem of dodgy thermostats on 944s again?
Alasdair

 
The plot thickens, or curdles or something weird . . .

Thanks for the offer Alasdair, but I don't think this is down to the valve. Driving to Birmingham last night I did get some heat out of the car, it took a while to come through and I didn't really have any control over it. Once on the motorway I could feel a suspicion of warmth through my gloves so I thought I'd play with the dials to see what would happen. It seems that at speeds of 65-70 or more there's plenty of hot air to be had, uncontrollably so with the fan running or not; at slower speeds than than that heat does come through if the fan is off, but once you switch the fan on the air flowing out is distinctly cooler. And the difference is pretty apparent between high speed / low speed.

I feel like I must be going mad - how can road speed have any bearing on the heating system? I'm sure this is no more ludicrous, so I'll mention it anyway: the engine is running hotter than it used to (top white line at motorway speed, before it used to sit about a third of the way up between the second and third lne and remain pretty static), is there a system where excess heat from the engine is dumped into the cockpit?

Cheers,

Neil
 
You need to bleed your cooling system properly mate. You have air pockets. When you are at higher engine revs i.e. at speed the pump is pushing the ccolant round the system and not at lower revs. I had a similar problem last year. Trust me a proper bleed will cure it. The heater matrix is just about the highest point in the system.
 
I was considering that may be an option Rob; there's been some occasional gurgling from down there recently. At least it should be a straightforward job to sort out.

Any thoughts as to how the air could have gotten into the system? Am I looking at a leak somewhere in the system?

Cheers,

Neil
 
They can be notoriously difficult to bleed mate. It may just not have been done properly last time by whomever it was doing it.
 
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