AC Compressor is on when heat is on?

I had noticed over the last 3 days using the heat on my Riv that the AC compressor is on whenever the heat is on. The outside temperature was around 48 degrees and I had the heat set to around 80. I noticed after I shut the car off you can hear the AC system pressure equalizing. And I checked this morning once I got to work and the clutch was engaged. I don't have the defroster on, just the heat. Is it suppose to work this way on these cars? I replaced the compressor this summer, it was bad last year so I would not have noticed it.

This is how it's supposed to work, unless you specifically set the 'Vent' button on the head. The A/C compressor runs to dehumidify the air coming into the car, even when it's heating. Until the outside temp gets below a certain point (40 I think). Then the compressor will not run.

Deek is absolutely right... The Vent button used to be called Econ(omy), because that is the only time that the system doesn't fire up the compressor.

Another bit of ECC trivia: Even though our systems have a Recirc button for manual choice, the computer will still recirculate if the inside/outside temperature differential is large enough, yet will ignore the Recirc button if the Vent button is selected...

Thanks for the info guys, good to know.

Eldo wrote:

Deek is absolutely right... The Vent button used to be called Econ(omy), because that is the only time that the system doesn't fire up the compressor.

Another bit of ECC trivia: Even though our systems have a Recirc button for manual choice, the computer will still recirculate if the inside/outside temperature differential is large enough, yet will ignore the Recirc button if the Vent button is selected...

This might be a stupid question, but how does the vent button work? Does it still use the heat if needed or does it just pull in the air from the outside? Also does the front defrost button also defrost the outside mirrors or do you have to use the rear defrost button? I usually always turn them both on, but i've always wondered.

98riv wrote:

This might be a stupid question, but how does the vent button work? Does it still use the heat if needed or does it just pull in the air from the outside? Also does the front defrost button also defrost the outside mirrors or do you have to use the rear defrost button? I usually always turn them both on, but i've always wondered.

Vent does use air from outside, and it still adjusts the blend-air doors automatically based on temperature - it just doesn't engage the compressor. Except for dehumidification, you could go all Winter on Vent...

If you have heated mirrors, they run with the Rear Defogger.

Eldo wrote:

you could go all Winter on Vent...

Maybe you could. But some of us are already feeling the heat come on in Auto mode and feel the need a few times already for the seat heater.

The point of both of my last posts is that Vent is automatic, and that the only difference is the compressor...
That's why the Auto light stays on, and the outlet temperatures and locations still vary according to your set temp. It works for everything BUT hot weather.

Are you saying that you've never tried Vent mode with the temp set at 75 or higher?

Eldo wrote:

The point of both of my last posts is that Vent is automatic, and that the only difference is the compressor...
That's why the Auto light stays on, and the outlet temperatures and locations still vary according to your set temp. It works for everything BUT hot weather.

I understood clearly the point of your last two posts. I was just adding my 0.02 in a tongue and cheek sort of way.

Are you saying that you've never tried Vent mode with the temp set at 75 or higher?

No I have never tried "Vent" over 75 that I can recall. I tend to use the Auto mode more than not. Except for certain days where everything is perfect and the sunroof is open and no humidity, then the vent comes on.
Usually have the sunroof open most of the time, even when the A/C is on or the heat is on, still like the fresh air from the roof and the sunshine to make me a Happy Boy.

Well now that we're moving into Fall, try Vent when you want heat with the roof open. You'll save a little gas, and wear & tear on the pump.

I'm with Rick - having the Auto mode on all the time. I do it for a few reasons:

1) It's an amazingly accurate HVAC system when it's working correctly. One of the best in the world, imo. Mine works flawlessly at 12 years old. Only problem I've ever had was a failed blower control module ($30 used part fix), and a few squeaks from the actuators, but they've magically quieted themselves down over the past 2-3 years.

2) Having the AC compressor on all or most of the time keeps the internals lubricated and fresh, which prohibits the seals from drying out, preventing refrigerant leaks. Again, the system is 12 years old and has never been recharged or replaced to my knowledge.

3) During my hypermiling experents, in my quest for ultimate fuel economy, I was able to enjoy very high numbers (high 30 MPH) with the AC running the entire time. I saw no improvement in turning it off. That's one of the benefits of having gobs of low-end torque on tap, I guess. The engine turns the AC pump without even realizing it.

Just my .02

Rick, I use vent mode unless it's over 80 degrees out or I get on the highway. I like to run with all the windows and sunroof open and not waste A/C efforts. This also works in cold weather - Vent only shuts the A/C compressor off, it will still control temperature in the cold weather. Also do this at least 30 minutes before arriving at the dragway, so you aren't the asshole dripping condensate water all over the track.

AA wrote:

Having the AC compressor on all or most of the time keeps the internals lubricated and fresh, which prohibits the seals from drying out, preventing refrigerant leaks.

I agree with the lubrication angle, and only God knows where the lube and wear curves cross... But I figure as long as the pump gets run a couple times a week it gets enough lube. In Summer that's no problem at all, and in Winter whenever the front or side windows fog up, I hit Auto or Defrost which fires it up again as well.

Quote :

During my hypermiling experents, in my quest for ultimate fuel economy, I was able to enjoy very high numbers (high 30 MPH) with the AC running the entire time. I saw no improvement in turning it off. That's one of the benefits of having gobs of low-end torque on tap, I guess. The engine turns the AC pump without even realizing it.

Well, it probably has more to do with the variable-displacement pump than the torque, but yes, this a very efficient compressor. I think I've only gained 1MPG by leaving it off.

But how about throttle response & belt wear?
I know this is a little too "be one with the car", and it doesn't bother me on the highway at all, but when I'm doing a lot of down-shifting and hole-shots around town, I can't help but think that the compressor doesn't like large, rapid RPM changes and that it is costing me a little oomph, too...

As long as you're using it every week, it should be well lubricated I'd guess. I'm just impressed at how long the system has held up being on more than 98% of the time for every day driving over the past 7 years.

Throttle response, I don't even notice the difference. Honestly I couldn't tell when the system is on or off by the way the car drives (maybe another good reason to mod?). Also, the AC clutch is supposed to disengage during WOT application. And as for belt wear, my last set of Gates lasted 90k miles. The accessory side could have gone further but I had a damaged supercharger belt, so might as well do both together.