A/C high side pressure switch NC or NO?

[MGM-2007]

My 2007 leaked refrigerant slowly and would not kick on when attempting to charge. Vacuum test confirmed a slow leak so I changed out compressor, accumulator, o-tube and low side pressure switch since it was cheap. Now holds vacuum but A/C clutch still won't engage. An open ground on the relay in the fuse box makes me think I have a bad high side pressure switch, but it's $100 so I don't want to blindly change it if there a wiring issue lurking. With the discharge line pulled and connector removed, I tested for continuity in the 3 pins of the switch. No continuity. Took my multimeter to the store to see if the new one had continuity between any of the pins. Nope.

Does anyone know the real pin out and test procedure for the high side switch? Most are normally closed and only open if there is or has been excessive pressure detected. Should I be looking for a certain resistance value instead of just continuity? Maybe the new one at the store was also faulty? Thanks

[sly]

If it's the same as 2003, NC. opens when pressure is high (>445psi) and resets below 260psi. Technically, it's not polarized. It should be closed like a switch (short circuit) under normal conditions. If the multimeter says 0 ohms, it's good. It's only purpose is to tell the PCM to kill the feed to the compressor clutch if the pressure gets high.

[MGM-2007]

2007 does not use that cutoff switch, it's a smaller one with 3 pins. But i still strongly suspect it should be NC. I never checked for continuity between the metal shell and any pins, only between the pins. I'll go back to that store that opened the box for me without me buying it, and test the pins to the shell. Or try one at another store. Hoping it's just a bad part at the store because one of the pins already is shorted to ground, so the theory that the circuit uses the shell as ground is pretty thin.

[sly]

In that case, I've got no clue. Getting the service manual with vacuum and wiring diagrams would probably be best. The 2003 Service manual says "normally open at 445psi and closed below 260 psi" so I'm not entirely sure that it doesn't require some pressure to close. If you had the manual for the 07 with that pinout, you could just jump the wires that make up the switch and get the compressor to kick on.

[jaywish]

That has me confused. Is it simultaneously closed and open between 260 & 455 psi? Maybe it is a Schrodinger valve?

[sly]

No. It has a large overlap like that so the switch isn't bouncing between on and off. It takes more force to switch it so there's a wide spread between states. Once it flips high, the pressure has to drop below 260 to flip back.

[jaywish]

OH thank you. That actually makes sense.

[MGM-2007]

Checked a high side switch at a 2nd store, also no continuity but figured I already blew $500 on the other components so what's another benjy? Installed it, no change. So NOW I'm willing to spring the $20 for the online manual. I lived and learned the C1081 shown above is the low side, not high side, is used on the 2007, closes at 42 psig and opens at 23. Jumped the lo side connector and clutch engaged this time. With old high side switch this did not happen so go figure.

On every other car I had, the pressure in the can was enough to kick on the cycling switch. This time the can would not start it, with 30 psig being well short of the required 42. I shook the can upside down, put it in a bowl of hot water, but could not get to 42 until I dunked the can, fittings and yellow hose down in a big tub of hot water. After a couple cycles the reaction could sustain itself and it charged normally. Ice cold A/c, just in time for September.

[jaywish]

Success!

[sly]

Wow. They made that setup a little too safe me thinks.

[DerekTheGreat]

...On every other car I had, the pressure in the can was enough to kick on the cycling switch. This time the can would not start it, with 30 psig being well short of the required 42. I shook the can upside down, put it in a bowl of hot water, but could not get to 42 until I dunked the can, fittings and yellow hose down in a big tub of hot water. After a couple cycles the reaction could sustain itself and it charged normally. Ice cold A/c, just in time for September.

This has been driving me nuts and making me think I have to leave it to an actual shop with a machine. The newer safety fittings on the can annoy me too, almost impossible for idiot me to figure out if stuff is actually being sucked out of the can. Older fittings? Compressor instantly cycled on, the can got cold almost instantly and I could feel stuff moving out of it in my hand. I'll keep the hot water thing in mind.

[gadget73]

the new ones do have a much lower flow rate than the old, must have something to do with that internal sealing valve. Have considered buying a side-piercing can tap to work around that issue.