1990 Caravan Heater

Could be just air in the system, which prevents coolant cirulation into the heater core.

Most obvious cause is low coolant or an air bubble, but if you've already checked and these are not causing the problem, then check the coolant/water valve in the heater hose near the firewall. I had this get stuck on an old

1990 caravan. You can tell if its stuck closed cause the hose will be hot up to the valve and then cool to the heater core. It is vacuum activated so check the hose does not have a leak also.

Good luck.

Bob

To determine if the heater core is stopped up...once the engine reaches peak temp feel the heater hoses going into the firewall, assuming that the heater control valve is working properly.(if equipped) feel the hoses going and and coming out, if one is very hot and the other is warm then you will have to have the heater core replaced

Check the air mixing door inside the dash. My '90 was blowing cold all the time, and I found 2 pennies and a nickle and quarter in there, stopping door from moving.

Coins got in via the dash vents above the cup holder.

After removing them, heater worked great.

You might want to try doing a backflush before replacing heater core. I had problem after coolant flush on a 2.5 engine with heater not blowing very warm air. First replaced thermostat which did not help and then did backflush. Heater works great now.

Thanks for the input. It turned out that the cable was not going in the sleeve all the way. After removing and soaking the cable in wd40 it seems to work fine now!!