Weird issue with AC/Defrost

[TCBRacer77]

So when ever I need to use heat and defrost my windshield, as soon as I turn the knob to full windshield the AC kicks on (compressor and all) even if the AC button isn’t activated. The control panel is breaks new do I already need a new one?

 

[TCBRacer77]

^1997 c1500 4.3 single cab

 

[someotherguy]

Defrost mode intentionally engages the A/C compressor; this helps remove moisture from the air the system is moving.

Richard

 

[AK49BWL]

I think it kicks on as soon as you reach the halfway point between floor and defrost in fact. And if you have the recirc button on, it will be forcibly disabled at the same time. Working as designed!

 

[TCBRacer77]

I think it kicks on as soon as you reach the halfway point between floor and defrost in fact. And if you have the recirc button on, it will be forcibly disabled at the same time. Working as designed!

Okay so this just means the original control panel I had must have been malfunctioning and I’m just not used to it lol. So is it actually okay to have my ac kick in like that if it’s super cold outside

 

[FullBlowncustoms]

Think my 95 K1500 kicks on and off for a bit. Never stays on with mine. I'm NO AC guy, but all my heat and AC has worked since day one that I've owned.

 

[Schurkey]

Define "super cold".

If it's cold enough, the A/C refrigerant pressure will be low enough that the low-pressure cutout switch will disable the compressor.

Is your low-pressure switch faulty or bypassed?

 

[mattillac]

How to: disable auto AC with defog

Something that's always bugged me since the OEM instituted it has been auto AC with any defog setting. So I usually disable it on my vehicles. My thoughts have always been I'll decide what the bloody car is going to do or what it needs based on the present conditions. I don't need some...

www.gmt400.com

Never got around to doing this mod.

Now the pictures are gone.

 

[AK49BWL]

How to: disable auto AC with defog

Something that's always bugged me since the OEM instituted it has been auto AC with any defog setting. So I usually disable it on my vehicles. My thoughts have always been I'll decide what the bloody car is going to do or what it needs based on the present conditions. I don't need some...

www.gmt400.com

Never got around to doing this mod.

Now the pictures are gone.

Yeah, only sad thing about remotely hosted pictures. I'll see if I can find my old control head later and put up some new pictures, if someone else doesn't get to it first.

 

[Schurkey]

Running the A/C when in "Defrost" has been a thing since before Fido's great-granddoggy was a pup. I learned about it in trade-school in 1980, and it was old-news then. I bet it dates back to the '50s when A/C was integrated into the heater/defrost system, instead of being an add-on in the trunk or hanging under the dash.

Defeating the A/C operation when in "Defrost" mode is nuts and counter-productive.

The A/C dehumidifies the air, which makes the defroster more efficient/faster/better. The "dry" air is then re-heated. Hot, dry air is better at removing windshield fog than hot, moist air.

The A/C compressor is protected against cold-weather damage by the low-pressure cutout switch, which also protects the compressor if the refrigerant charge has leaked-out. It's a well-thought-out system.

Screwing this up makes no sense at all.