Car heating problem for you mechanics out there

Before I peruse the Jeep forums, I'll throw this out here. Girlfriend has either 2000 or 2001 Jeep Grand Cherokee. When heat and blower fan are engaged heat comes out of the two dash and one foot passenger side vents but only cold air comes out of the two center dash vents and the driver's side dash and floor vents. Any idea of the problem and how expensive it might be to take to the shop and have it fixed? I had just assumed that heat was equally funneled away from the engine to all vents but apparently there must be some distribution system.

Probably an obstruction like a rats nest or a dead cat. Any unusual smells?
Don't laugh this happened to my dad. It is winter and you might not notice the smell till spring.

Check for vacuum leaks (bad ends on rubber tubes--normally you will hear some hissing from the leaks--start the engine up, set the controls to heat, then turn the engine off and listen for moving air). Many vehicles always have the heater core hot, but use doors to mix hot and cold air.

Grab the heater inlet/outlet lines... If the engine is well heated, controls set for heat, both hoses should be pretty warm--one may be warmer than the other. If both hoses are cold, or one is warm and the other cold--then you have a water flow blockage... Look in the radiator. Is there lots of rust (can block heater core)? If no rust, is there a lot of white power/deposit on the ends of the water tubes? If so, then the heater core may be blocked... If not, perhaps a heater hose has collapsed or the liner has failed. Is there a water valve to let water through the heater? Is the valve opening and closing?

Other possibilities, bad water pump (sometimes, water pumps just "stop" pumping at times--they look OK, but replace and everything works again). or rusted metal tubing to rubber hose connection (tube/casting filled in with rust).

Thermostat OK? Closed when engine is cold, open when the engine is hot (radiator stays cool until the engine heats up, then radiator gets "instantly warm").

Lastly, is engine running OK? Any missing, or excess pressure in the radiator system (sometimes smells like tail pipe of running engine). Any oil/moose looking foam in radiator? Could be a blown head gasket or other oil/combustion leak.

If none of the above, see if you can find a maintenance manual (library, dealer parts counter) for your car--The newer cars with electronics everywhere may have a debug/error indicator if something is wrong.

-Bill

1.Check that the controls for the heat are actually activating the vent opening/controls under the hood or see if a vent may be stuck open, sometimes they are controlled by aircraft cable.
2.Do you have the option between having recycled cabin air or a mix of outside and inside cabin air? I would think that there would be a mixing system but maybe the vents in question are fresh air vents and not actually heat vents but choosing the recycled cabin air control may solve the problem by closing the outside air vents.

Best of luck

Thanks for the advice thus far. I should add this. Engine seems to run ok and temperature gauge goes up to about half way which she says is normal. In the little time I observed the problem, it seemed that the working side (passenger) got warm pretty quickly, especially considering how cold out it was today but it wasn't blowing out quite as much air as the non-heating side which was cranking out plenty of air just no heat to it. Problem occurs whether vent is set to circulate inside or outside air.

Try here: http://www.heatertreater.net/Grand Cherokee Blend 98-04.html

The Cherokee is built with Blend Doors to control the heater and AC function. The controls are either dual control for separate passenger/driver control or a single control system. The doors are controlled by a stepper motor that seeks an open and close setting every 20 times the Jeep is started. During this calibration routine the motor is overdriven creating excessive force on the components. The end points for open or closed are set by a plastic pin that is part of the plastic door assembly. When this pin breaks, the stop points become the open and closed position of the door. Eventually, the doors will break(see picture). The most common fail mode is for the broken door to fall to the bottom of the box, blocking the heater core NO HEAT

Frankvz is probably right. I am not sure if they are stepper motors or more like a window motor, but either way that seems likely.

The second challenge you discussed - not enough heat when it is really cold - is a slightly different problem. Modern engines are much more efficient and lower HP than in the past - meaning they produce less waste heat. The higher coolant temps also make the radiators more efficient.

Sometimes - on very cold days only - it can be useful to block off 1/2 of the radiator with some cardboard. Make sure the coolant in the radiator is full - not just the extra tank.

FRANKVZ said:

Try here: http://www.heatertreater.net/Grand Cherokee Blend 98-04.html

The Cherokee is built with Blend Doors to control the heater and AC function. The controls are either dual control for separate passenger/driver control or a single control system. The doors are controlled by a stepper motor that seeks an open and close setting every 20 times the Jeep is started. During this calibration routine the motor is overdriven creating excessive force on the components. The end points for open or closed are set by a plastic pin that is part of the plastic door assembly. When this pin breaks, the stop points become the open and closed position of the door. Eventually, the doors will break(see picture). The most common fail mode is for the broken door to fall to the bottom of the box, blocking the heater core NO HEAT

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blend doors,,
I am a jeep owner also

Yep, blend doors.

My '03 Ram has 'em and has had a fault which corrected itself.

I'm waiting for the other shoe to drop...

Lasernerd said:

blend doors,,
I am a jeep owner also

Click to expand...

Yep, the damn blend doors, about $1,500 to fix. There is a DIY kit out there the works well but makes the system a single zone instaed of a dual zone, I'll look for a link to it.

Thank you for all your posts and FrankVZ for posting the link. One question: As this is a Limited Edition, I assume it's a dual zone? Are the blend doors only located near the dash as explained in the DIY kit that FrankVZ posted or are there any in the driver's side as well? The link said the most common problem was to lose the heat in the passenger's side first but this is the opposite.

When I see the car again, I'll see how easy it is to remove the glove compartment and look at the doors.

Lasernerd said:

blend doors,,
I am a jeep owner also

Click to expand...