islaTurbine

Ok, please don't excoriate me too much on this....

I'm considering simply leaving the A/C switch (and thus the compressor) engaged all of the time for the remainder of summer. Will this create any mechanical/maintenance issues by doing so? Will it be hard on the A/C compressor if it is left engaged during engine start and engine stop? I've always turned the A/C off on all of my vehicles a few minutes before I shut off the car in order to try and let system temps equalize in order to prevent mold/mildew growth inside the system.

My 928 is incredibly finicky on getting the compressor to engage due to the microswitch on the HVAC control. She's a 1978 so accessing and removing the HVAC is not an easy task, otherwise I'd do so to try and resolve the issue.

FWIW, the A/C was redone about a year ago with a Griffiths system and is running R12 freon. She blows super cold when I'm successful in getting the microswitch to engage the compressor.

Thanks all.

joejoe

I cannot see a problem with left on all time. While I turn mine off less than a mile from home to cool the system (is an **** thing and not sure if it makes a difference other that in my head) there should not be a concern. (of course I could be wrong )

merchauser

I have often wondered the same thing?

worf928

Not an issue really. If you are worried about mold/mildew spray some lysol (or other similar agent) on the evaporator and then spray rinse it with water at the end of A/C season. (Do this after first vacuuming out whatever accumulation of stuff is on the evaporator.)

EDIT: you will ‘use’ a little more battery ‘juice’ when you start. 3A for the A/C clutch plus whatever incremental current is needed for the couple-hp to turn the compressor. If that’s a problem then you’ve already got a problem.

FredR

My ac is pretty much on all the time and I do not switch off the thing for starting purposes.

I have never tested it but my understanding is that all non essential circuits are bypassed during cranking. Whether the ac clutch solenoid is bypassed I do not strictly know but I am pretty sure the blower is bypassed- either way 3 amps for the solenoid compared to the ampage of the starter is irrelevant or so I would think..

islaTurbine

Yeah the additional amperage required was the first thing that crossed my mind. My understanding is that most, if not all, “modern” cars have a bypass when cranking the engine to start. It’s just that my car was made in 1/1978 so I’m not so sure that “modern” applies to her.

docmirror

The circuit for the AC clutch is not engaged when the key is in the start position. I haven't checked the print to confirm, but I'm pretty sure it's not active during engine crank. As for running it all the time while the engine is running, there's no problem with that at all.

islaTurbine

@docmirror
Are you making your way to ATL this weekend for the big event? Bring the Bonanza; I live near Falcon Field and will pick you up.

PorKen

I would like a relay for the A/C to shut off at WOT or at very engine speed*.

78-79 have a special relay for RPM cutoff but I imagine it was later deleted because you might want A/C at full throttle on the Autoban?


I did this on my old GMC diesel - soon to be upgraded to a timed off relay.



*S4-up, I could do this via the LH with a code patch and output from the unused pin-25 with a relay bypassing the CE-plug wire to the compressor (87-89 M12, 90-95 E11).

docmirror

I'm flying to Bartlesville OK to shop for houses. Visiting my kid. ATL is pretty far, and no way I'm gonna fight my way into ATL - evar...

captainOCD

I thought I'd add a datapoint to this. I normally shut off the ac when I park in the garage, so I can't give comment on cold starts. When coming out from running into a store or something though, if I leave the ac engaged the motor cranks much slower than if I disengage the ac before cranking. So I try to remember to turn off the ac before starting.

islaTurbine

Thanks. What year is your car?

captainOCD

86.5 US 5L 32V. A/C system is running R134a.