Hello, my in car heater will only pump out hot air and it's getting a bit too much to cope with when the weather is warm! Can someone tell me what is the problem? is it a thermostat somewhere? The car is a 1983 MK1 Golf GX.
The heater controls are run by cables. There's one cable that runs from the controls to a valve on one of the heater core hoses in the engine compartment near the firewall. Sometimes the cable will kink inside the dash and get stuck, so when you slide the lever it doesn't move. Or sometimes it will just stick and you can't slide the lever.
I'd start by trying to close the valve under the hood by hand, if it still moves (isn't stuck) I would pull out the heater controls:
On your car you would pull out the stereo, then remove the cover plates that go around the switches on each side of the instument cluster, remove the screws from under there. Remove the heater control levers by pulling on them, then remove the heater control plate, it should pry out with a flat screw driver, and under there should be another screw. The screws that go upward into the dash at the top come out, and then unplug the switches, remembering where each plug goes. You should now be able to see the heater controls, and see what works and what doesn't. 2 screws pull the controls out of the dash for a better look. Probably a stuck cable.