Is the air conditioner compresor on when the heater is on?

Re: Is the air conditioner on when the heater is on?

> But traditionally

That's a matter of perspective. Step back years earlier. The original definition matches what Toyota uses now.

> how does the Prius work this out?

First, note that you can have air blowing on the windows to clear them without the need to use the defroster. This is a little known efficiency benefit for those not acquainted with the HSD Prius. And it works surprisingly well.

Second, it takes very little to create cold air in the winter. So that compressor doesn't have to work much at all to remove humidity.

Third, the steering-wheel button makes flipping the defroster on for just a moment a snap.

My question to you is what kind of vehicle do you used to own and where do you live? Never have I ever had the need to turn on the A/C during the dead of winter. The ordinary defroster has worked just fine here in Minnesota. In fact, one time I was dumb enough to find out just how hot I could get the interior of my Dodge Omni. When it reached a 90 F degree difference, I decided to abort. It was hot enough to vaporize any humidity, removal wasn't even neccesary.

I suspect short-trips work differently. I try to avoid those, especially in the winter.

 

umm your statement that winter air is "already dry" is a bit presumptious.

all air when heated will have their moisture content reduced by increased rate of evaporation. to add moisture when heating would just fog up the inside of your windows.

i for one, (living in the pacific northwest) welcome the reduced humidity that heated air provides. and yes the Prius will expend some energy to heat up that air. but that is the way it works.

also air conditioning doesnt actively remove moisture from the air. as the temperature of air is reduced, its ability to hold moisture is also reduced causing condesation on the coils of your conditioning unit. minimal cooling (and i would assume this to be true in the winter) would result in minimal reduction in moisture content.

 

the compressor does not run all the time even in the summer.

 

the air conditioning is thermostatically controlled. and the compressor does cycle on and off according to the demand for cooling in the Prius.

now it is my understanding that the duty cycle of the compressor when the air conditioning is running full blast is less than 50%. this is done to prevent the coils from freezing up... for a better illustration, take a look at the duty cycle of frost free freezers that also only run at 50% and then "idle mode 20% and defrost 30%.

 

nope

 

not very likely... as i said, the air conditioning is controlled by the thermostat.

check it out one day on a semi warm or cool day. set the temp to something like 75º or something. you will notice although the fan speed is steady, the air will cycle from very cool to luke warm. that is from a low demand for cooling. if the demand is low enough, eventually the cooling coils will be warm and not condition the air at all. it is just that a car retains heat so poorly that it doesnt remain at anything resembling cool most of the time if there is any sun out.

you realize it only takes less than a minute to cool the coils off to the point that they will instantly form ice on the coils. to prevent ice build up, the compressor cycles to allow ice to melt off and drip away.

if you remember the old window mount air conditioners always dripped water outside. that is the result of the coils defrosting. this is also why air is conditioned. it is the instantaneous freezing of the moisture in the air passing through the coils.

to prevent buildup, the compressor cycles on a predetermined schedule that pays no heed to cooling demand of the air conditioning system. this prevents excessive buildup that will kill the cooling capacity of the system since ice is only 32º and the coiling coils are much much lower than that...(usually in the range of -40º F)

 

Re: Is the air conditioner compresor on when the heater is o

I don't believe this is a correct statement. My wife's Subaru (and other cars) turn the A/C on anytime you have the system set to defrost. I suppose they could have some special system to make sure no bad things happen.

 

because the Prius is controlled by the thermostat, what ever needs to be running is running. if heat is needed, then heat you will get. if cool is what you need, then cool is what you will get.

worrying about wasting energy using the air conditioning in the winter time is something you really shouldnt be concerned with.

i guess we are all guilty of assuming that air conditioning only cools... but ones that heat are fairly common in central climate control systems that have been in houses for years. now does that mean one machine does both?? nope... cant be done. but it does mean that one button, or one switch or whatever controls both by endevouring to maintain the temperature you set. i simply is more efficient and cheaper to combine the two systems.

i had a car where the air conditioning would have run like you describe... cooling off the coils even if the temperature was 40 below outside. those didnt have a thermostat. they only knew two things, that was on and off. the rate of cooling was controlled by the fan speed. whats worse, the air conditioning button was right next to the power button for the radio... cant tell you how many times i turned the d**n thing on by mistake.

thankfully, we dont have to deal with that kind of stuff anymore.

 

Just for comparison, my wife's car is a '97 Subaru Legacy L wagon. Nothing fancy, 1 step up from bare bones.

 

Re: Is the air conditioner compresor on when the heater is o

For long A/C sytem life and to prevent leaks, run the A/C at least once a month including the winter. This rule is true for all cars. The description below only applies to expansion valve/ receiver systems that have cycling compressors. (Almost all foreign cars). Cars that have Fixed Orifice/ Accumulator/ Constant running compressors have similar issues but the rule still applies (almost all american cars).

The system is full of refrigerant, oil, and unfortunately, air, water, and impurities. The air won't cause a problem if it is dry and there is not much in there (like a properly charged system). Same with the water. However, the water tends to condense inside the lines and corrode the seals in the compressor and otherwise (again, there is not much water, but it IS in there). The Receiver/Dryer contains a dessicant material that will absorb the water, and the oil will lubricate the seals at all joints in the system and in the compressor, at the compressor shaft seal, and will flush physical impurities out of the Thermostatic Expansion Valve (TXV) and into the Receiver/ Dryer. A properly charged and running A/C system (even while the compressor is cycling) has the Receiver/Dryer full of liquid. At the bottom of the Receiver/Dryer (it's a cylinder, mounted vertically) are all the nasties, like water and impurities. They only stay there if the system is running! Otherwise, as the pressures even out (in a system that hasn't been used for a while) everything gets everywhere, except the oil, which you want everywhere, it tends to pool, and the seals dry out and are free to be attacked by the air and water.

If you run your A/C once a month, every month, including winter, you will likely NEVER have a problem with your A/C, it will probably NEVER need service of any kind.

Nate

 

Re: Is the air conditioner compresor on when the heater is o

When I lived in Michigan without a garage, my defroster worked much, much better with the A/C on. Why? There was always humidity that could be removed, it got in the car via my snow on my boots if not the intake grill under the windshield wipers. The A/C system generated a lot of heat, so it caused the car to warm up about twice as fast.

The strange thing about living in Grand Rapids is that nobody lived far from work. We spent a significant portion of our gasoline warming up the car. Perhaps we couldn't tolerate the 30 minute commute becoming 2 1/2 hours in bad weather, plus 20 minutes for warmup and scraping.

Nate

 

The Prius aircon uses CO2 as refrigerant. Check out the Denso Site.