L400 AC problem

[Blue2009]

I have a 2002 L400 with some AC problems. When running the front AC the air blows cold, but if I turn on the rear AC the front gets warm and the rear is cold. If I switch everything off and go back to front only it will get cold again. I read on the L300 that there’s a timer that switches the system back and forth to maintain both. Is this true for the L400? Is there a test point or way to check this timer, and where is it located?

 

[kbrown934]

Step 1. Make sure system is full. Check for bubbles in sight glass. Get a matched pair of thermometers so you work with good data. Numbers matter.

 

[ShelbyD]

I have a 2002 L400 with some AC problems. When running the front AC the air blows cold, but if I turn on the rear AC the front gets warm and the rear is cold. If I switch everything off and go back to front only it will get cold again. I read on the L300 that there’s a timer that switches the system back and forth to maintain both. Is this true for the L400? Is there a test point or way to check this timer, and where is it located?

Sounds like low refrigerant level to me. Mine was a can low when I received it, would still sort of work intermittently but after adding almost a can it’s now much better.