Jeep Owners!

[JakeC]

I've been searching for a while now, trying to use all outlets to try and find a solution.

I have a 1997 Jeep Grand Cherokee Limited. I replaced the heater core last year around February.

Recently while my brother was driving the Jeep on the highway he noticed that it wasn't blowing hot air anymore. He told me about it the next day, and I checked it out while the car had been running for a while and engine temperature was normal. Inlet and outlet hoses seem to be warm while the vehicle is on. I've also noticed the "gurgle" of air in the system after replacing the heater core. I figured it was normal and had never had a problem with heating before, though it did take a while (10-15 minutes) to warm up in the cabin.

The heater blows fine, but there is cool air coming out of the defrost, and hot air blowing out at the bottom (All while set to just defrost). When I change it to other settings, it seems to switch and blow from the correct areas.

I've narrowed it down to:
Blend door problems.
Air in the coolant system.
Vacuum hose problems.
Thermostat problems.

I'm a pretty novice mechanic and sort of learn things by trial and error when they happen to break on the Jeep. I've obviously replaced the Heater Core and I've performed the 249 to 242 swap as well as other minute things. I replaced the thermostat yesterday, and tried to "burp" the system. The jeep stayed warm for around 5 minutes and began blowing cold air again. Engine temperature was normal as well. I also pulled out the glove box to check for any kinked or damaged vacuum lines, and found nothing out of the ordinary.

Just curious if anyone has had this exact problem before? I've seen a lot of variations of these problems on other forums, but where would be a good direction to keep moving?

Thanks a lot.
-Jake

[TheEnemy]

I had the same problem in my 84 CJ. The problem was that one of the cables (temperature control) had come detached so it wasnt getting air throught the heater core but was just circulating it. My "fix" was to adjust the door manualy and leave it that way (always full hot).

There is a big difference in age and model so I cant say if yours works the same way as mine.

[JakeC]

Actually, I may have figured it out. It's a common problem with the Grand Cherokees. I pulled a code from the HVAC system, and I guess it's a blend door issue?

[JakeC]

Well, after digging into the dash and removing all of it, the motor that controls the blend door for the automatic temperature control had a plastic gear inside of it that was cracked.