So every year I forget about this until it starts to get cold out. My heat in my 98 Ram 1500 quad cab doesnt work worth beans. Here is what it is doing:

Once the engine heats up, I turn the heater on. it blows hot air for about 10 seconds, then the air goes to warm, to cold. Even with the heat dial cranked all the way to the right. If i turn the heat back off for about 5 minutes, I can turn it back on and again get about 5 to 10 seconds worth of hot air before it starts to blow cold again.

What could be causing this? the engine is getting to temp at 190 degrees, it has a new thermostat but still I get no heat. Does the same thing on defrost too, blows hot air for a few seconds then its just cold air coming out of the defrost vents.

Does anyone have any ideas? I've already checked all the vaccuum lines under the hood. checked the fuses, checked the relays, checked the wiring connectors on the heat box i can access from under the dash. I'm stumped and im cold!

 

check the blend door.... there is a coupler between the little motor that runs it, and the lever that is attached to the door. They are known to break...

Check the hoses for the heater core. If one is warm, and the other is not..... you have a blockage. Try backflushing it to clear it.

Burp your cooling system. Might be air trapped in the heater core.

 

and where is the blend door? fairly sure i dont have air in the system. I recently replaced the water pump and i made sure there was no air in the system when i re-filled the radiator

 

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Sounds to me like you have a partially blocked heater core.

 

Here's the replacement coupler, it has a video you can watch to see where its at. Basically right under the center console, where the hump in the floor is.

http://www.heatertreater.net/Dodge%20Product%20Page.htm

 

Heh heh. You said *hump*.

 

before you go ripping your dash apart try back flushing it first


I was in the same boat as you until about 2 weeks ago when i flushed my heater core and changed my thermostat...

discontect the inlet and outlet hose
let the core drain
blow it out with an air compressor... fill it with CLR and let it sit for 2 hours
blow the clr out with air compressor (it will be foamy be careful)
rinse with water in both directions until the water runs clear
connect the hoses back to the engine and "bump" the system

there are some good youtube videos that will give you a better visual

I now have the cab roasting hot in about 5-8 minutes and have to turn my heat off after 15 because it's soo hot

 

ok. didnt have any CLR handy, but I did back flush the heater core. I disconnected both the in and out flow lines. extended the inlet line with a piece of PVC pipe into a bucket, then i first blasted 120PSI of compressed air thru the system from the outlet tube. (my logic being if it was blacked the blockage would be easier to force out the way it had come in). got some lovely brown colored fluid out of it, but nothing that looked solid or sludgy. So i switched to water. I happened to have a hose adapter i had bought for another project (beer brewing related) that didnt work out for what i wanted it for. But it fit perfectly inside the heater core hose. So i shoved it in there and clamped it.

Cranked the hose up full blast and ran a good 10 gallons or so thru it. Water came out clear. So I hooked everything back up. fired up the truck, burped the system and turned on the heater.

It WORKS!!! Well, at least its pumping out just heat now. its no longer blowing hot for a few seconds then going warm to cold. However its not super hot. my Wranglers heater is way hotter than this, but hey, at least its heat! thanks for the help guys!

 

If it isn't real hot, then there are either other blockages or the thermostat is partially clogged/failed.