Heater problem

I have a problem with my heater. I think it doesn´t blow as hot as i should. I have flushed the heater core and the whole system and checked the valve. Both hoses going to the heater core are hot to touch, one a bit hotter than the other.

Is there some flap that lets air go around the core? And what is the flap under glove box in front passengers foot space, and when shoud it be open? Mine opens only when I set heater control to off-position?

Engine temperature is normal, so I don´t think it´s the thermostat...

Any ideas???

just a thought, make sure you have good vacuum at the control valve under the hood. the vacuum line on my 88 is purple. mine did the same thing a while back. also check the hoses one of them might have collapsed. good luck.

under the dash on the passenger side make sure a wire or something hasnt gotten the way of cable. Possibly hendering it from fully opening the flap

I have a good vacuum to control valve, but my valve closes with vacuum and is normally open. Valve works fine, I took it off and washed and tested.

So there isn`t any other flaps but the one under the dash on the passengers side? And it should be open on defrost and heat modes too??? Mine opes just fine but only when I set heater control to off-position...

I'm on my second XJ, first an 88 now a 90 and have had heat problems with both. Seems to be getting good flow through the heater core but the air is cool. It gets hot only when I put it on bi-level and then it's only hot comming out of the vents, the floor is still cool. Sorry I can't help, but I've been researching this for about 4 years and no one seems to have a silver bullet =(

Hekuliini --

I'm sorry that I am traveling at the moment and I do not have access to my factory service manuals. However, I believe your suspicions are correct. The Cherokee heating system uses vacuum to control a series of flaps, or dampers, in the ductwork under the dashboard. The temperature of the heated air is not controlled only by the flow of coolant to the heater core. The Cherokee system is what ventilation engineers call a "variable volume" or "variable air volume" system, which means that the temperature is regulated by mixing a variable amount of outside air with the air that flows through the heater core.

I think you need to open (or remove :scared: ) the dashboard to check for good vacuum at the little motors which activate the flappers, and to be sure the flappers move freely. I don't think you should attempt this without the detailed information in the factory service manual. Many of our members have this, so perhaps someone could copy those pages and send them to you.

OK so I found one vacuum diagram which includes all flaps. It seems to me that the faulty flap would be the one called blend air door and it´s the one before the heater core. Only problem is that in this diagram that I have this flap doesn´t seem to be vacuum operated??? Is there some wire or what???

HEKULIINI said:

OK so I found one vacuum diagram which includes all flaps. It seems to me that the faulty flap would be the one called blend air door and it´s the one before the heater core. Only problem is that in this diagram that I have this flap doesn´t seem to be vacuum operated??? Is there some wire or what???

Click to expand...

It's cable operated, the switch that you slide left/right on the heater control for cold/hot, operates a sleeved cable to open and close the blend door, you should be able to see it very easily under the dash without removing anything to verify that its hooked up and operating.

Josh

OK! Thanks!