A/C confusion

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Sep 11, 2019 | 03:55 PM

#16

jurish

5th Wheeling

Joined: Oct 2007

Posts: 47

Likes: 3

From: Texas

Quote:

Originally Posted by charles adams

When I run my front a/c unit (dash) I'd say the cool air is a 6 out of 10, but when I run the front a/c and the rear a/c together, my cool air in the front is a 8 out of 10.... what can I do to get the front unit to function colder without having to run both units?

I can confirm this phenomenon in my 05 X. I actually measured the drop when I turned on the rear AC. I think what is going on is that with the rear AC off, the expansion valve back there is closed and the system becomes unbalanced. There is no fix. If you look at the schematic for the system, both front and rear evaporators are just "T'ed" with no real way for the refrigerant to decide where to go. If you just run the rear fan at low, that should be enough airflow through the rear evaporator to keep the expansion valve open and the system balanced.

Sep 11, 2019 | 07:11 PM

#17

01__Excursion

Cargo Master

Joined: Nov 2017

Posts: 3,110

Likes: 540

From: Rock Hill, SC

I had pondered this exact scenario, but you are correct without the rear fan running, the TXV closes, and in effect should prevent the excess refrigerant needed to saturate the rear coil and simply have it sitting in waiting from the Tee back, meanwhile the front system should have what it needs to operate prior to the tee off to the rear. Still doesn't explain the situation unless there is a slight low charge, or an air flow issue through the evap coil which would cause improper TXV operation.