Yet another AC cold driver/warm middle/hot right thread

[haigha]

I've been searching around the site for a while and I see this is a common air conditioning problem. I've read a lot of threads and the Bentley AC section but haven't come up with anything definite to swap out.

2004 4.4 ~24k

I recently replaced the cabin air filter and the FSR--this fixed the problem with no airflow at all.

Both driver and passenger settings are 60 degrees (also tried 70). The ambient temperature is around 90. I've adjusted the dial on the middle vent from 3 blue dots to 1 blue dot and it does not change the symptoms.

Symptoms:

- Air on left vent is cold but perhaps not as cold as it should be.

- Left side of middle vent is cool, not as cold as the left vent.

- Right side of middle vent is warm, perhaps ambient temperature.

- Right vent is about the same as the right-middle vent.

- Rear seat vent is about the same as the other warm vents.

Here's what I've checked so far:

- No codes are being thrown to my CarChip. No Service Engine Soon light.

- R134a was checked by mechanic about three weeks ago at oil change. I don't think R134a has ever been added.

- The glovebox and rear panel fuses are okay.

- Compressor sounds like it is engaging. There is a medium-high pitched pressure sound when AC is turned on, not overly loud. It is masked when the fan is turned up to about half speed.

- Aux fan spins when AC is turned on.

- I swapped the cables on the IHKA (climate) control module--passenger to driver and vice versa--to make sure it wasn't a bad connection. Because of the limited play, it was tough to swap them. I'm not sure if the sensors are further along the line or are in the IHKA itself.

- Cleaned out the vents on the climate control module intakes on the IHKA with a compressed air can.

- Looked and listened for any leaks in the engine compartment. I didn't hear anything but I can hear the compressor working.

My (relatively uneducated) guesses are:

1. Passenger Heater valve (engine compartment, left strut tower according to Bentley).

2. Evaporator temperature sensor. Is this close to the FSR? Perhaps it got dislodged when swapping out the FSR? But wouldn't that affect all vents the same?

3. IHKA heater core sensor. Since swapping the cables didn't have any effect, I don't think this is the case but if the sensor is what the white cap plugs into, maybe that's what I need to swap?

4. A motor / valve is not closing properly on the passenger side. I'm not sure what the most likely candidate is here.

Do you have any thoughts based on your experience with this or a similar problem?

Thanks.