I have a 95 E420 that is not cooling properly at idle and with high speed fan settings.

Using a thermometer with the a/c set on the coldest setting and low fan speed I read 40F on the center or side registers on a 90F day at idle.

On Auto speed or high fan it will drift up to 80F on the center or side registers

If the car is moving I get 40F on low fan and about 55-60F on high fan/auto. Movement appears to help some.

My clutch fan and both electric fans are operating properly for engine temp and a/c usage. My R134a is at the proper level as well. Sight class looks normal.

I am reading about a monovalve on many models but the descriptions are confusing. I read about a Repair kit and to look for a dime sized silver cylinder with 4 blade screws. I have located an inline valve with 4 blade screens on the firewall passenger side with a 3" tall quarter size silver cylinder that is HOT when the engine is warm which makes sense being inline with what appears to be a heater core line. I can't explain why its bigger than a dime but parts searches do refer to it as a ACC mon valve.

When I removed the silver cylinder the inside did not readily look like the repair kit.

Can I have some direction on what I am actually tampering with and if I am on the correct trail?

Thanks!