no heat blows cold air

[BULLDOGBW]

I have replaced the water pump and thermostat. Now the temp guage rises then lowers. its running hot then cold and the heater is blowing cold air thanks again.. BULLDOGBW

 

[Potomac30]

Did you get all of the air out of the system?

 

[DeRocha]

If the heater fails to blow heat when the thermostat is in the normal range your heater core is most likely plugged. (easy fix).

 

[BULLDOGBW]

think i have it fixed.

i flushed out the whole system then put zerex radiater cleaner in it. it says to drive it for 3 to 6 hrs. i dont drive it for long trips so i will leave it in for a couple days. it is blowing hot air now. it worked better than i thought. thanks for your help.

 

[DeRocha]

Glad to hear its working better...

If it still gives you trouble then I'd seriously consider swapping out the heater core. Other threads contain info on replacing the heater core. Lots of good info and pics, plus it is an easy job.

 

[exlporer]

I have been trying to figure this out on a friends 94 sport. We have replaced the waterpump, heater core, all hoses, as well as the (vacuum exchange valve) before the heater core. When the vacuum line is plugged in the air blows cold but if you unplug the vacuum line the air gets warm again. Any idea why the valve is staying shut when it is plugged in? The valve is obviously functional.

 

[FR-425]

vac valve

Hey Explorer

If the vehicle has a vacuum actuated heater control valve (vacuum exchange valve)

it uses vacuum to hold the valve shut as you described,

when you set the in cab control to "heat" the vacuum is released and a spring inside the valve opens the valve.

So if you have continuous vacuum at the valve, the control is bad.

They do it this way so that the in dash control unit is Less likely to cause a vacuum leak effecting engine performance and emisions

I did not know any 94's had vac valves most I have seen are cable pull.

Temporary fix is to unplug the vac line form the valve and plug the vac line with a bolt for the winter. Full on heat though!

But Sporties come with windows right?

 

[exlporer]

Wow! Thanks FR that helps so much. Starting to lose my mind. It's a project so not a big deal.