AC blows cold going down road but hot in traffic or redlight to redlight.

ID Status Date Year Make Model Transmission Type A/C Controls Public/Private
#14450 Closed 2004 Chevrolet Silverado LT public

I have 2004 Silverado LT trim crew cab 5.3 engine if that matters. Late last summer started having ac issue, driving any speed 10 miles and hour and above the ac out all vents blows nice and cold air(according to thermometer in center vent 38-40 degrees), I’ve had one in my trucks for 40 years. When you get in stop and go traffic or from red light to red light the temp slowly climbs to 80 degrees out of all vents. Start moving a steady speed or rpm around 1000rpm and it starts blowing cold again. Had compressor, accumulator/dryer and orifice tube replaced in September issue stayed the same. Took to a regular ac shop instead of my regular mechanic ( he did run pressure test on compressor and head pressures were outta whack therefore the reason for replacement, plus 325,000 miles on it figured why not) for a check up and they diagnosed it with a bad blend door actuator bad( Center actuator). Over the course of winter it developed a roar like a crop duster starting up under the dash when recirculating button was pushed and fan on levels 4&5.
Yesterday I got the hair brained idea to go ahead and replace the 2 actuators that are a snake to get to, the one the ac shop diagnosed ,the top one, and the fresh air one.
Got it all out, replaced and back together and still have the same problem. Drive down the road and it’ll freeze you out on level 3, level 4&5 are now normal noise levels, but pull in the drive thru at Sonic and the temp starts climbing from 38 to 70 degrees out of the vent. Water temperature just as a FYI never rises above 210.
I know there are 2 more actuators on my truck, one on passenger side above transmission tunnel and on driver side in same general area that I plan on replacing in the next few weeks but am looking for advice, help or insight on this issue.
Wondering if it could be the controller in the dash, mine is dual climate with 2 dials to set temp to a specific number and has console with 2 vents to blow in rear seat.
I took a 5-10 minute drive rpm was steady at 1200, speed 40-45, engine water temperature 200-210 outside air temp 90 degrees with 47% humidity. Air temp via thermometer in center vent was 38-40 degrees. Pulled in driveway parked in shaded area and put in park rpm dropped to 700ish within 2-3 minutes air temp from middle vent was 80 degrees. Popped hood to satisfy my curiosity and the clutch was engaged and running on compressor. Also on a lark decided to run water from garden hose over radiator and condenser was about 5 degree or less drop in temp in air from center vent.


Okay, I really need to see what the a/c pressures are during the various conditions to be certain but I believe you have one or more of the following faults.

The system is overcharged with refrigerant.

The engine fan clutch is not working properly.

The airflow through the condenser and radiator is restricted.

Refrigerant flow through the condenser is restricted.

The pressure with center vent temp 38-40 degrees
Outside temp is 89 humidity is 72%
Low pressure was 45
High side was 155
This was going down the road at 30mph

Sitting idling
Same outside conditions as above
Vent 75
and climbing
Low pressure was 52ish
High pressure was 155-160


I will stick with the original diagnosis starting with checking the refrigerant level and purity.  In both scenarios the low side pressure is too high. I would be looking to see somewhere between 18 and 35.

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