Heater fix. Did I miss anything?

[jamnett]

My son's '88 LE puts out hot air for about 10 minutes then goes cold and the AC is cold at first but then gets warm. Using the helpful postings and the shop manual we've checked resistance while sliding the heat control button and it does what it should. Also put in a new heater relay. The water valve under the hood operates and the small levers under the dash move when we slide the heat control. My son is driving it now and I won't know if it's ok until this afternoon. If it still doesn't work right I guess we will take it to our local "Toyota only" repair shop. Is there anything else we can do ourselves?

[wiccanferret]

Does this car, by chance, have the push-button fan controls?

[fredk]

is the engine temp staying up?

[es250nut]

Originally Posted by jamnett

My son's '88 LE puts out hot air for about 10 minutes then goes cold and the AC is cold at first but then gets warm.

Sounds like you may have two similar yet separate problems. As you noted in your post, the slider (if it is the pushbutton type control panel) very well could be responsible for the heat cutting out. I have found that if the A/C charge is somewhat low it will allow the system to work for a short bit then the coolant gets too warm and won't compress back to a liquid thus making the A/C stop working.

[jamnett]

The engine warms up and the heater blows hot air at first. After about 10 minutes at highway speed the air goes cold but the fan still works. There's a good chance the AC problem is coincidence and it just needs a re-charge.

[jamnett]

Yes, the fan control is by push buttons.

[fredk]

is the engine temp staying up?

[Kep]

Just a guess but you mention that it occurs at highway speeds. I'm with Fredk, it the engine temp staying up? If your thermostat was stuck open it would allow the coolant to get too cold, especially at highway speeds.

I believe all toyotas have a view port on top of the freon drier. If you see bubbles while the unit is running it is an indication of low freon. Are you still using R12? If you have converted to 134A then there are lots of other considerations depending upon what was done during the conversion.

Kep

[toyomoho]

Check the position of the arm on the heater valve when the air coming out is hot and cold. Perhaps the climate control system is malfunctioning and turning this valve off.

When the AC air goes hot, see if the compressor is still running. If the Freon is low the compressor will stop operating to prevent damage.

Sometimes the expansion valve in the A/C system freezes up after short time due to moisture in the system freezing. This stop the flow of Freon.