89 celica intermittent heater problem

[crabberjon]

Please help. I have a 1989 Celica GT Convertible auto trans. with the push button type heat a/c controller. My problem is that when I drive the car in the summer the heat works fine if you have a cool night you can adjust it however you want. In cold weather the heat will work at times only if you have pushed the buttons previously and set the temp to full heat, if you try and change the setting it will stop working for a while then sometimes 25-45 minutes later it may start working again. I don't know if there is a thermostat involved on the control panel there appears to be some groves and a small round hole in them that could be something to do with a thermostat, I'm guessing. Please let me know if anyone has figured this one out? Other than that at 160k the vehicle runs like a top and gets over 30mpg, it's just really cold inside at times.

[toyomoho]

The heater control valve may be defective. Look in the engine compartment for coolant hoses entering the firewall; one of these should have the valve on it. The heater core may also be partially plugged. You can attempt to flush this using a hose at one of the core entry hoses.

When you find the valve you may be able to watch its operation. Thus use the heater controls and see if the valve arm moves when it is supposed to.

If this is an automatic climate control system there may be a thermostat to regulate temp by opening and closing the valve. Or the heater controls could be defective.

But start with the heater control valve.

[Rick89GTS]

Classic 4th Gen intermittent heater problem.
Usually results from cracked solder joints in the heater control panel:
http://www.st162.com/forums/viewtopi...ghlight=heater