is running the AC with the window open bad?

[The motor guy]

I was curious you know how people are sitting in the drive through and they leave their windows open or the people that have their door open when their hooking up a trailer. Is that bad for the air conditioner to do that? Wouldn't it cause the pressures to get real high in the system since it has to work much harder to pull the more moisture/heat out? Or does it not make a difference?

 

[The_Jeff]

I like how you think. But if they shut off the AC then started it later wouldn't it be even worse?

This happens every time you start a cold (warm?) car.

 

[The motor guy]

I don't have anything against running the ac with the windows open I was just wondering if this is bad for the system. Then again I rethought this question and when you keep it on fresh air mode I guess its cooling the outside air all the time anyways. So this was a dumb question. Nevermind.

 

[Chris142]

Wont hurt a thing.

 

[Rix]

Harmless.
the engineers are good enough to prevent cars from damaging themselves during normal, even often times ABNORMAL operation.
Most cars produced in the last, oh, i don't know, 30 years or so, have some sort of pressure switch to prevent such things from happening.
Thermostatic cooling fans, electric cooling fans, etc, also help with keeping pressures (related to temperature) low enough to be "safe".
I severe hot weather, some a/c systems might shut off due to overpressure sitiuations, but they should be able to keep up.

just having a window open or what have you, will have no negative effect besides letting the cool air out of the cabin.

 

[SteveSRT8]

Back in the old daze we ran our ac in convertibles at the lights when stopped. Especially nice in a black interior.

 

[Torino]

Originally Posted By: motor_oil_madman
I don't have anything against running the ac with the windows open I was just wondering if this is bad for the system. Then again I rethought this question and when you keep it on fresh air mode I guess its cooling the outside air all the time anyways. So this was a dumb question. Nevermind.
There are no dumb questions--just dumb answers John--Las Vegas

 

[glum]

Oh, there are dumb questions. Oh, yes, yes, yes there are. I asked one once. No giveaways but it started with "Will you ma..."

 

[Rix]

Originally Posted By: SteveSRT8
Back in the old daze we ran our ac in convertibles at the lights when stopped. Especially nice in a black interior.

Pretty much a neccessity when it's 90+ with the sun beating down on you.

 

[cmf]

Running the AC full blast with the windows open is exactly the same as running the AC full blast with the windows closed. If you have a temperature sensing AC then that's different but either way the AC is not going to blow up from running it with the windows open.

 

[The motor guy]

I see. Well thanks for the responses.

 

[mechtech2]

Not efficient, for sure.
But no harm should come of it.

I don't know what leaving a door open while hooking up a trailer means with respect to this.

 

[Nick R]

Can't imagine it would hurt it. I do this all the time, and especially with our mustang convertible. The only thing that bugs me is that at idle, I've never seen a car that cools particularly well.

 

[Craig in Canada]

The load on the system will be higher. Every automotive AC system has a feedback-loop controlled evaporator valve. The evaporator is maintained slightly above freezing (so it can't freeze up - duh

and the control system allows for a wide variety of operating conditions - low fan, high fan, hot weather, cool weather, humid, dry etc....

AC system "load" comes in the form of heat, humidity and volume of air. Condensing moisture out of the air releases a lot of heat into the system, cooling the air obviously does, and drying/cooling a higher volume of air requires more energy than a lower volume. This variable valve will need to open more in higher load conditions, thus allowing more liquid refrigerant into the evap coil, thus flowing more refrigerant, thus releasing more heat at the condenser. All of this requires more refrigerant flow, more compressor operation, more energy, and raises under-hood temperatures.

Is it "bad" for anything? The system should be designed to handle this, but it would be wasteful to do this unnecessarily. The "system" wouldn't see it any differently than starting up a car which was parked in the sun.

 

[Craig in Canada]

Originally Posted By: cmf
Running the AC full blast with the windows open is exactly the same as running the AC full blast with the windows closed. If you have a temperature sensing AC then that's different but either way the AC is not going to blow up from running it with the windows open.


Generally in what I'd consider high heat/humidity, recirculation modes should be used so that the moisture only gets removed from the air once. Most temperature-controlled systems do this automatically without telling the occupants. Running recirc with the windows closed is much easier on the system than running outside air with the windows closed. It also uses less fuel since the compressor runs less because less work is being done by the AC system.

 

[Hokiefyd]

Originally Posted By: Craig in Canada
Generally in what I'd consider high heat/humidity, recirculation modes should be used so that the moisture only gets removed from the air once. Most temperature-controlled systems do this automatically without telling the occupants. Running recirc with the windows closed is much easier on the system than running outside air with the windows closed. It also uses less fuel since the compressor runs less because less work is being done by the AC system.


I've been doing this for years now, and for the reasons you listed. The system has to work much less to cool air that's already been cooled (and dehumidified). The sultry 90-95*F air around here with dewpoints in the 60s and 70s is worst case for an A/C system. I'm sure it's even worse further south, in places like southern Georgia and Florida.

Both of our cars now have automatic climate control systems, and both run in recirculation mode more often than not, and by their own choosing.

 

[glum]

Yeah, NC summers are not the stuff that AC system longevity is made out of. Ask me how I know.

Originally Posted By: Craig in Canada
Generally in what I'd consider high heat/humidity, recirculation modes should be used so that the moisture only gets removed from the air once. ... Running recirc with the windows closed is much easier on the system than running outside air with the windows closed. It also uses less fuel since the compressor runs less because less work is being done by the AC system.

I tend to prefer pulling in outside air just out of the paranoia that I/we may be breathing in fumes or other bad stuff and it will simply recirculate throughout the car (and therefore also our lungs) for the duration of the trip. Or do the systems actually always pull in a certain percentage of outside air, even on "recirculate" mode? I had one vehicle (can't remember which) whose manual stated that this was the case for that vehicle.

 

[MarkM66]

How many people need to say it's okay?

 

[cmf]

Originally Posted By: Craig in Canada
Generally in what I'd consider high heat/humidity, recirculation modes should be used so that the moisture only gets removed from the air once. Most temperature-controlled systems do this automatically without telling the occupants. Running recirc with the windows closed is much easier on the system than running outside air with the windows closed. It also uses less fuel since the compressor runs less because less work is being done by the AC system.


Very true, didn't think of that scenario. I was talking along the lines of outside air and not recirculation. That's odd too because I pretty much only use recirculation since I live in Florida.

 

[mechtech2]

Not all AC systems use a 'feedback loop', whatever that is.
Many use a constant orifice.