Hot air always blowing from vents. Can anyone help?

[stan]

This is actually the case on my '98 528, but I imagine that the principle would apply across the board to one degree or another.
I can put the temp on 60 (and yes, the vent dial is on COLD too) and it always blows warm to hot air. The engine temp dial has no problem getting to the beloved half way mark and never goes past it, so I'm not sure if it's a stuck T-stat or not.
Any help is greatly appreciated.

[Gooch]

If it was bad t-stat the car would either overheat or not get up to temperature.

[stan]

If it was bad t-stat the car would either overheat or not get up to temperature.

Right....thus I was almost sure that it wasn't the T-stat.
Not familiar with the part you've mentioned. Can you elaborate some please?

Thanks.

[John 535is (Sydney)]

Sounds like either the controls not sending the signal to the heater control valve, or the heater control valve itself. On the 535 model, there are 3 wires to the 2 heater control valves (1 valve for each side, therefore 1 wire plus common). Unplug at the heater valves and put a meter across them. You should see the pulse signals to the heater valves change as you move the temp setting to different temperatures. You should also here them chattering if they are still plugged in. If you see (or hear) this, your controls are working, so the only thing stopping the heat from turning off will be the heater valves. On mine you can actually pull them apart, they are just solenoid type valves. There is a needle inside with a spherical pyramid type base (the tap valve). If the needles are stuck or broken, thats your problem, if not, you are probably going to replace the valve units.

I replaced the circulating water pump under the valves while I had them out becuase both my valves were full of gunk, so chances are the pump was too.
(PO had used some sort of additive to hide the head gasket failure, which eventually clagged everything with goop, (so techncial!)).

John 535is