Well, I flushed the heater core, got heat. Then I drove about 12 hours, felt the heat going down on me slowly so I just flushed again. Hopped back in the truck and now I have ice cold air coming in on me after the truck has fully warmed up. I thought it was still plugged up, but then I noticed that as I drive the heat comes on. When I stop, even at a light, I can tell that the air coming from the vents cools off considerably. Any ideas what might cause this?

 

If you flushed out the heater core and its still not hot you may need to replace it. But first the system uses doors to switch the heater to ac and vents. Make sure yours are working properly. Are you haveing a problems with the vents not putting enough air out at the front vents. If so you may have a vacuum leak. Check all hoses.

 

Not having a problem with the volume of air, just the temperature. The vents switch back and forth through the settings with no problem. The temperature is great when the truck is moving. When I stop though, it cools down a lot. Just replaced the water pump, thermostat, and temperature sensor last week.

 

I read through the autozone service manual for heater core replacement. Sounds like a lot of work, of course. But it said to "properly discharge the air condition system". That kind of worries me, do I need to be discharging the air conditioner?

 

you may need to release the gasses in the a/c unit because you will have to pull the condensor. depending on where and how long the lines are.

 

When you flushed the heater core, did you reverse flush it or "flush" it by putting water through it the normal-flow? (FYI, the water for the heater core flows from the water pump through the heater core, NOT through the heater core to the water pump)
If you didn't, you should have reverse-flushed the core, otherwise you probably shoved contamination further into the core, possibly effectivly plugging it up.

Also, check the hoses for the heater core to make sure they aren't kinked or clogged. Also, the fittings on the water pump and engine for the hoses.
Check your coolant level (engine cold, radiator should be full, and coolant reserve tank "full").
A crappy thermostat?

 

Yes, I flushed it reverse first, then normal, then reverse again. I drove it for a while then heat dissappeared again, so I flushed it again. I think it is possibly plugged and I need to change the core. While I am in there I am also going to check the condition of my evaporator coil (?) because I know I have a very very slow leak in the AC.

 

I know you said that you changed the thermostat, but it sounds like it's stuck open...it does happen with new ones. Before you go tearing out the heater core ( a lot of work ), I'd try another thermostat.

 

I went through 3 thermostats on my 96 dakota once before I got a good one. No more autozone junk since then. If the core was plugged, I don't think it would blow heat at all, or maybe blow heat while stopped, not driving.

 

Thanks guys. I do get great great heat when I am driving so I am going to go to NAPA and replacew the thermostat. I am losing faith in every part I buy from Autozone. If I can't buy a decent hose clamp from them why would I expect to get a complex part like a working thermostat from them? Sorry, I digress, but I have been getting fed up with these poor quality parts lately.

I will post back and let all of you know the results. I had no idea that people were getting bad thermostats.