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
Amb. 84F
Low 20psi
High 212psi
Vent Temp 58F

So I added 134a until I got the following:
Speed 1700 rpm
Amb 84F
Low 30 psi
High 275 psi
Vent temp 55F

@idle:
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.


Thanks for any thoughts.

 

Controlled by a thermostat built into the clutch. What engine?

 

'07 Expeditions are all 5.4 V8.

-- Chuck

 

Engine is 5.4L all stock, all original except for one new plug coil, idler pulley, minor misc. A/C control panel was replaced under warranty at 35,000 mi.

 

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.