I've got an 86 gxl 5 speed, no major mods.

A few weeks ago, my heater started doing a weird thing, and still does it consistently.

The heater will blow hot air into the cabin, cosistent with the temp of the engine, (luke warm eng.= luke warm air / hot=hot) But once the car is at full operating temp for a few minutes, the air from the heater goes cold (or at least as cold as the outside air)

It gets weirder, because after driving for another 15 min or so, the heat will come back on, and work like it should. WHAT IS WRONG WITH THIS THING?
its starting to get really cold at night, and will be freezing soon, i gota have heat!!

 

well you could try flushing the system or maybe your heater core is going bad

 

I thought it could be the heater core as well, but its a VERY consistant pattern, all of a sudden, from nice warm heat, to ZERO heat, in less than a second, which doesnt seem like a clog to me.

 

Number one, make certain the cooling system is full. Turn the ignition to on then slide the temperature selector from hot to cold or visa versa. You should hear the door motor running. If not you logicon is most likely broken. If you hear the motor continuously operating, it could be a ground. The reason I state the last possibility-when my car was new, the door motor would keep operating. After the dealer replaced 3 logicons, they finally found a bad ground, and that fixed the problem, at least for the last 14 years. if the logicon is bad, Icemark will do the repairs.

 

sounds like a bad logicon, that has a loose face plate screw that is rolling around and shorting the circuit board

 

i dont think its a loose screw in the logicon, because of how consistantly it switches from hot to cold as the car reaches full temp/ does it every time at exactly the same time. any more ideas?

 

It can be the blower. My 87 n/a does the same thing. Put the heat to the max on the logican and the fan power to off. The heat will gradually increase the faster and longer you drive.

 

Well he says that the heat stops when the car is fully warmed up. The above ideas can't be it becuase if it were the blower motor, there would be no heat.

The first thing that popped into my mind was that its his thermostat or some ****. I mean when it opens the hot coolant thats now in the engine circulates through the radiator. At this point his heat probably goes cold becuase the hot coolant inside of the heater coil is now circulating back into the engine and through the thermostat back into the radiator. Maybe its staying cold becuase his engine is overcooling, via a bad fan clutch?

lol, all speculation, but you wanted ideas.

 

I had that problem in an 86. I took the logicon apart and resoldered the solder joints. (cold solder joints cracking and losing conection seems to be a common 7 problem) Everything worked fine after. All I could figure was that something would heat up and lose the connection. After it cooled down it would make the connection again. BTW: I did the same thing to my wiper control board and regained the intermittent setting. Do not try these repairs unless you know how to handle a low power soldering iron, or you will destroy the circuit boards.

 

my heater doesnt even work, Not even air coming out when i switch it on. some one told me it might be my blower motor