heater only works sometimes?

[davandsarah]

Heres the deal, its a 1987 toyota celica gt, the heater will work great for a while, the blow cold, then maybe awhile later decide to get hot again. There is a valve on the firewall that controls wether the antifreeze goes into the heatercore or not, this appears to frozen when I grab the cable going into it, I'm wondering if this is something I could take apart and service, the car was stored winters for 5 years so the heater wasn't used much, maybe this added to the problem, it appears as though the valve is controlled by cable, but I'm not certain if its vacuum assisted liie some vehicles, any help would be appreciated, its still cold in Wisconsin. thanks

[Pineapple]

The cable is move by the control inside by moving from heat to cold. Put the control at cold, check the valve position, move control to heat and see if the valve changed. Also check coolant level. A coolant flush may help.

[89_3SFE]

Sounds like you've got the same problem that I had on my 89 GT. I have since found out it's the wiring behind the heater control panel and all you have to do is either find a replacement at a junkyard or pop it off and resolder everything on the backside. I just temporarily fixed it by placing a wooden block behind the radio where the lever shifts when it goes to cold. That way, when the car tries to shift to cold, it can't and the heat stays on.

[maxaud]

if that doesn't work try your thermostat maybe?

[89CelicaGTTurbo]

i have the same problem, it sucks.

[bashattitude]

Just to eliminate one of the common reasons for warm air to change to cold air check the overflow tank once the car is COLD if it is empty you are low on coolant (there will be a little bit in there) there should also be a low mark on the overflow tank as well. But back to the common reason... low coolant in the system creates air pockets that travel through the system hence the reason it comes and goes. So if this is the case simply add coolant to the overflow tank BEFORE you let the car cool down, as the car cools down it pulls coolant back into the engine to replace what it pushed out when the car was warm.

[GA_Wolf]

But one thing you may check while the engine is cold..I repeat for safety..cold!
If your overflow is empty, check the level in the radiator...it should be full, like Bash said when the coolant cools it will draw from the overflow to keep itself full. If it's not, you may be extremely low on coolant (causing the heater symptoms noted). Fill your radiator with coolant.....run the engine for a minute and chack and refill if needed. Then put the cap back on and run normally. As the coolant heats up it should go into your overflow...then when the engine is hot, check your overflow level and fill it to the correct amount.

[davandsarah]

Coolant level is good, the problem lies somewhere in the cable/valve set-up that controls the flow to the heater core. Last night when I was driving and the heat started working good, I got out and zip-tied the linkage on the valve in the position it was in while the heat was working, it works now but it will be on HOT all the time, I still need to figure out what to fix.

[thousand_five]

air lock.... or clogged heater core