I just bought a used 02 Ram and the heater isn't working like it should. When I first turn the fan on it will blow hot air for about 5 seconds then it cools off. If I turn the fan off for a few minutes and turn it back on, the same thing happens. The a/c works fine, just not the heater. Any ideas what might be the cause?

 

SEARCH funtion. Type in Blend door.

 

I think it may be the blend door. I know my mode 1 door is broken, air only blows from the vents no matter what the setting is. I suspect the blend door is broken too. I don't hear it change when i change from cool air to warm air, but i can get warm air briefly though so I'm not sure whats happening.

 

Ok, so here's an update on this issue. I ordered a Heater Treater Blend Door and when I disassembled the dash it turns out the blend door is fine and working properly. My next thought, as some of you suggested, is a clogged heater core. However, both heater hoses get hot, so I'd think the heater core would be ok, correct?

Thermostat has also been metioned, but it reaches operating temp just fine.

What should I do, go ahead and flush the core and replace the t-stat? Look somewhere else?

 

I would do a cooling system flush. Maybe just do the heating side. That may get things moving. Pull both hoses that go into heatercore off the block and hose out that way. It is possible its clogged.

 

Another update, flushed the heater core, but it didn't change anything. Still blows hot for about 5 seconds then cools off.

Also, should my passenger floor board be wet after the flush? It appeared to be only water, not coolant. I thought maybe water got through the opening in the firewall where the heater core ends come out. Or could it be worse, like a leaking core? I haven't noticed any coolant smell or wet carpet before the flush.