Warm A/C 91 500SL

[Ron MB]

While driving and under hard acceleration then letting off the gas a squeal is heard coming from under the hood lasting only 5 seconds or so, then the A/C blows warm air for a while then returns to the 70 degrees.
This problem does not occur all the time. Not sure what is happening.

Checks I’ve made.

• Performed the A/C pushbutton Control module (Self Test). Code 01
• Next test, all potentiometer and feedback potentiometer read normal.
• Replaced receiver dryer, vacuumed down the system for 45 min. no leaks. Did not replace the expansion valve it’s a little difficult to get at.
• Re-charged the system R-134a, approx. 29 oz. And replaced the oil PAG 4oz.
• Ambient Temperature (Fahrenheit) 90, Low side 40, and high side 250.
• Checked the Mono Valve default (voltage applied valve closed, also clamped the hose).
• No difference. With blower high speed Center vent Temp. approx. 69 to 72 degrees F.

All the above checks seem to be normal???? With exception of the vent temp.

This is the only symptom that I know I have. Any help or inputs would greatly be appreciated.

Thanks In advance, Ron