I got the car to run after it was sitting for 2 years. The heater was working perfectly fine until 2 days ago. i checked the fuse and reset the heater relay. Still didn't fix it. I think the heater core is clogged. How do i unclog it??? What do you guys think caused the problem?
thanks...

 

Remove one of the hoses and turn the heater on with the car running... If no water comes out then its definately clogged...Even though I wouldnt know how it would clog, but just give it a try.

 

i have the same problem.... today i warmed up my car and the heater worked fine then while i was driving it, it was blowing cold air. could that be a heater control valve?

 

ok, does the heater blow, but just cold air??,sometimes the linkage for the heater control hot/cold, under the dash can fall off, ( had it happen once) its hard to explain where its at, looking int he factory service manual is the only way to know where it is...

 

The FSM says on the inboard side of the heater box, you will find this:

 

so i basically need to rip my dash apart and take a peek in there

 

revhi..have you had any coolant issues with your car..check the coolant level and make sure that it is up..i replaced my coolant recently ..and when I did I encountered and "air lock"..which gave me cold air at the heater..I took the cap off and ran the car ,,letting the temperature go up and open up the thermostat and kept squeezing the bottom and top rad hoses to "burp the system..Don't know if this is your case..but usefull info any how.sorry to thread jump...

 

i tried every method possible: i took one of the hose off and let the engine run, used the flush kit, still doesn't work. Fuse is fine. I will have to replace the heater core or make the plate open all the time. Would the 1990 heater core wiring plugs be the same as the 1987???

 

today i will try to replace the heater core. hopefully, it will work.

 

so i took off the dashboard. 89 and on heater core plugged in perfectly. Yet, i still have no heat. i was frustrated for a while until i discovered my thermostat was broken, so i replaced it and oh boy i have heat now...problem fixed. My idle was at 2700rpm before, but now it dropped.