General Heater help, please...desparate!!!!!!

[ozfish]

My 1999 2.0l EL with climate has just decided to blow out cool air no matter what temp the display is showing. Up until now it has been fine. The heater fan etc all work fine. The top hose in engine from rad to block is hot and so is the bottom return hose to the rad. The engine temp guage will hover at 90 and the rad fan works. I took off the rad expansion tank cap and revved engine which caused some coolant to come out suggesting the water pump is ok.
There has been no coolant loss and the oil level shows no rise or water in it suggesting a blown head gasket ( I always fear the worse ! )
As the cold weather has now come I'm desparate to sort this out asap.
Anyone have any suggestions as to what it may be,
A faulty thermostat in the engine ?
A blockage or air lock ?
Or a fault in the control panel ?
Any advice or suggestions please as to how to fix this would be very much appreciated.
Thanks,
Oz.

 

[ozfish]

Just to confuse matters-
I cleaned the cabin temp sensor as it was full of fluff. It spins when ignition on so seems to at least work that way.
I have noticed that when the car warms up the heater is ok and warm air blows out, then when the engine reaches operating temp the heater just blows out cool to cold air despite display showing upwards of 22 degrees.
Any recomendations as to where to start ?
Thanks.

 

[jasonh131]

i had to earth the chips on control panel to reset the intenal temp sensor...

 

[ozfish]

Thanks Jasonh131. Trouble is how exactly did you do it and what chips/where on the panel etc. I sent you an e-mail earlier re this asking for your advice as it would be greatly appreciated to sort this fault.
Many thanks,
Oz.