compressor runs on heat setting

[rydeon]

I have a 2000 chevy astro basic work van. The ac clutch cycles on and off repeatedly even when i do not have the ac on. It stays on for a long time causing the drier/filter? to ice over. Is this normal?? Thanks for any info.
-Paul

[WoodButcher]

It's my understanding the comp comes on at the defrost setting as well as AC but I don't know why. Maybe someone here can educate us both?

[Mmusicman]

A lot of people from "up north" have never experienced what it is like to be in a heavy afternoon torrential downpour rain in sweltering hot weather in the southern tropics.... where you're windows can steam up big time in the heat of the day with the humidity! You absolutely need your defroster with A/C cold air!

But having the A/C always on with the defroster in the winter time is also absurd! Unfortunately there is no way to separate the two functions... in GM's infinite wisdom.

It drove me so crazy that I finally put a cut-off switch to the compressor, so I can control whether the compressor kicks on or not... in ANY position!

Ironically, the A/C compressor does NOT kick on if you use the REAR A/C only, without using the front as well. I wound up personally putting a "signal" connection from the rear a/c fan switch on mine, so I could run the rear without running the front. I find it nice to be able to have cool air gently cooling from the back only, on those days where you want a little cooling of the entire van, but not blowing cold right on you. The vents in the Gen II's really suck compared to Gen 1! I've tried using the defrost vents for gentle cooling purposes without blowing directly on you, but with high humidity and dew points, the windshield just frosts up. So this was my solution.

Regarding the stock factory control:
The first 3 settings are compressor ALWAYS ON .... Max, Normal, and Bi-Level.
The next 3 setting are compressor ALWAYS OFF .... Top Vent, Heater Vent, and Bi-Level.
The last setting Defrost, is compressor ALWAYS ON.

I suppose if you want defrost without A/C, you use the bi-level (defrost and heat vents)

I like the way the Imports do it... with a manual lighted switch to turn on compressor... regardless of air control settings! Simple and easy!

In my photo here... the left LED indicates my electric fan is on, and the right LED indicates when my A/C compressor is on. (I need to change it to a blue LED). It lets me know when the compressor is engaged or cycling.

My modified "A/C Bypass" switch is the "rear wiper" switch... which I converted. I've never used or needed rear wipers! (learned to drive with mirrors, plus I can still see fine out back window even when raining).
* Switch (bottom position) is A/C compressor off.
* Switch (middle position) is A/C on/fan on (normal).
* Switch (top position) is A/C on/fan off (highway).

The electric fan should normally ALWAYS be on when the A/C is in use. The condenser ALWAYS needs air moving across it, or your high pressure side will overload. I use the "electric fan A/C signal off" only when traveling on highways, where condenser gets full air flow from air coming in at highway speeds. The fan is still controlled regardless by the electronic thermostat, and typically comes on when idling or driving slow... regardless of A/C signal.

What can I say?
I like being in control, and I like knowing when things are on or not.
It just took a few relays, diodes, and some wiring...

[rydeon]

Thanks for the great info. I have heard about the compressor running on the defrost setting before. But mine runs even on just the Heat setting and the vent settings on floor or mix or any combo for that matter. Also the intervals between the clutch being on and off get longer. Starts at about 12 seconds on and 12 seconds off and then get longer as the van runs. Sorry about the ignorance but this is my first operational(kinda) ac system. I always had cars with this stuff deleted. If this is normal im fine with that it just seems odd.

Thanks again for your time!
-Paul

[WoodButcher]

Lol MM, thanks.
I don't use the rear windows either, I catch hell from the bride all the time because my interior rearview mirror is covered with post it notes.

[Mmusicman]

...I catch hell from the bride all the time because my interior rearview mirror is covered with post it notes.

LOL!!!

[Mmusicman]

My "rear defrost" button (which I also have NEVER used) ... I plan on converting to a latching "FORCED AWD" or manual 4x4. I don't trust the controller in hard 4x4 applications, and don't like the idea that a tire has to slip before the AWD is engaged. Seems like that might be hard on the clutch-pack inside the transfer case too. The button latches already, lights up, and resets with the key off. I'll put nice "factory looking" labeling on them. I'm re-purposing these buttons because I like the factory look, these controls aren't used, and it's in a convenient obvious visible location.

Next "might" be the "rear heat" button which I have never used either. I don't have any issues with it, but no specific plans either. Last year it got cold maybe two days, and I still have a very capable front heater. As long as the A/C is functional... I'm good!

Note to the OP: If your compressor is engaging in the vent and heat positions, then something is crossed somewhere. This shouldn't be happening. My guess... the issue "might be" the signal switch in control panel itself. There is also a relay under the hood that "might" possibly be defective and sticking? But for now, if you don't want the compressor coming on, you might even pull that A/C relay until you find the problem. It would be a "temporary" work-around.

[rydeon]

That helps. I will pull the relay like suggested. Thanks again.

[tanvanmanwithaplan]

Regarding the stock factory control:
The first 3 settings are compressor ALWAYS ON .... Max, Normal, and Bi-Level.
The next 3 setting are compressor ALWAYS OFF .... Top Vent, Heater Vent, and Bi-Level.
The last setting Defrost, is compressor ALWAYS ON.

This is great info. The way the van works is pretty weird. I want to be able to run defrost with no AC and also recirculate heat to warm up the van more quickly without running the compressor which is something I used to do in the winter using the MAX AC setting before I fixed the AC. So I am going to add a compressor defeat switch. I think I will use a rear hatch release button from an older van I pulled from the junkyard since that spot is a blank on my 2001

[MountainManJoe]

It’s on for good reason. I’d leave it. The engineers know what they’re doing. My buddy disabled his and then had to spend several grand to replace the entire system.

[tanvanmanwithaplan]

I am an engineer.

It is stupid that they did not make a separate recirc button from the Max AC setting. And engineers both do not always know what we’re doing and often are not actually in control of design/functionality decisions like that

[MountainManJoe]

If you're an engineer then you should know it takes less energy to heat dry air.
You can recirculate heat easily I don't understand the problem.

[tanvanmanwithaplan]

It takes less energy to heat dry air, yes. But it does not take less energy to run the AC compressor to dry (AND COOL) the air and then heat it, especially when running the compressor costs fuel and the coolant heat is wasted energy otherwise.

Many other vehicles have the controls set up in the way I am describing. It’s not a novel concept.

Cheers

[MountainManJoe]

Most people don't want humid air blowing on their cold windshield. I'm sure you know what will happen.
Compressors are incredibly efficient these days. The fuel consumption is insignificant. Most people would rather have HVAC that works.

Set controls to MAX-AC, and turn temp dial to hot. Now have you have recirculating warm air. What's the problem?

[tanvanmanwithaplan]

Max AC doesn’t blow on the windshield