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Diagnosing Taurus no A/C

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Before diagnosing Mom's '02 Taurus warm air A/C issue I watched a video which gave advice to check the fuse, relay, refrigerant and clutch, so here's how it went...

The issue...room temp air comes from the vents when set to Max A/C and dialed to full cold, and warm air comes out when dialed to full hot. There is no sense of cold air at all.

fuse - confirmed continuous by multimeter
- with no key in the ignition one of the a/c fuse's terminals in the engine bay fuse box read 12+V and the other 0 V

- refrigerant - a quick press of the schrader valve reveals refrigerant pressure in the system

- compressor and clutch - the middle of the compressor clutch wheel turns when just a little force is applied but does not spin freely
- When the engine is on and A/C turned to Max A/C, the compressor clutch has a pattern of engaging for just over 1 second and then releases for about 5, and repeats this on 1s off 5s pattern without interruption for 5 min while I observed.

- relay - the video suggested testing the relay junction but the owner's manual doesn't show any of the engine bay relays labeled as being associated with the A/C, so that was a dead end. The clutch seems to be working ok so I'm guessing the relay is a non-issue.

As I'm testing I notice the engine light is on where I hadn't noticed it before. Called Mom and she says it wasn't on before, so I guess it just tripped. DTC code reads P1633 which translates to 'keep alive power voltage too low.' Battery failed last month so it was replaced with a brand new one from Wally's.

The only observation I can offer other than the above is that when the A/C is turned to Max and the compressor is doing it's 1s on 5s off pattern, during the 5s it's disengaged you can hear a faint scraping sound presumably coming from the compressor clutch that sounds like two very flat surfaces, one being spun and the other not, and they're barely touching. It doesn't make the sound during every 5s disengage interval, but it's definitely there. It seemed to show up more the longer the A/C system ran. The sound stops when the A/C control panel switch is turned to off.

Could this be a bad pressure switch / sensor?

I'm all ears

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