07 Expedition w/aux rear air, 172,000 mi, well maintained.
92 deg days in south Florida I'm noticing A/C feels warm at idle but not bad under speed so I took some readings:
Engine off: 90 psi low & high, Amb 84 deg (Gauge Manifold is Mastercool brass)
doors open, a/c on max cool, fan high:
Speed 1500 rpm
Vent Temp 58F
So I added 134a until I got the following:
Speed 1700 rpm
Low 30 psi
High 275 psi
Vent temp 55F
Low 40 psi
High 250 psi
Vent temp 59F
While @ idle or slightly higher I heard the fan clutch kick in (and wind noise), immediately the head pressure dropped to about 190-200psi, low dropped to 30 psi, and vent temp started dropping to 50F and below (48F) but didnt stay more than a few minutes.
Engine off, new high/low pressure is 96F w/ amb of 83F.
At ilde it almost looks slightly over charged. Shouldnt the fan clutch remain on at idle? How can I check or is it better to just replace? Not sure what cycles it, engine coolant temp? refrigerant head pressure? is there a way to test? IT was spinning the whole time while taking readings but there was a noticable change when it kicked in.
Try using a fan to push air accross the condenser to check the pressures. I think the new models use electonically controled fans. My 08 F150 had a pair of wires going to the fan drive. The clutch fan may be doing what it is designed to do.