AC and wasted gas


#1

I have a '08 Toyota Corolla, and it appears that the AC compressor comes on whenever the defrost or defrost/heat setting is utilized, (that is, when the fan is turned on, dialing the defrost w/o the fan does not seem to activate the compressor). Had a '03 Corolla and the same thing happened, I hoped Toyota would fix this “feature” in the 5 year interim. Why does the copressor come on? I know it helps clear the windshield for m/b 30 secs., but then it is not needed! I love this car, but the 1.8 L engine is a bit underpowered w/o the compressor running, and it drives me crazy to be running the air-conditioner in the middle of January and having to override the AC effect w/ heat and wastes gas. Setting the dial to defrost w/o the fan on is not enough to keep up with condensation on the inside. Is the compressor coming on, and is there anything I can do?


#2

I think most modern cars do this, I believe three of my Hondas (Civic, CR-V, and Ridgeline) all do. It is used to dry the air to keep condensation off the windows. It also helps keep the seals in the compressor lubricated during the winter months when the A/C isn’t used as much. In addition, I believe it takes something like around 8 hp to run the compressor which in my experience hasn’t used that much more gas. In my 1989 Honda Accord for example I got 24.9 mpg with the windows down and 25.5 mpg with the A/C on instead.


#3

ihave the same thing on my montecarlo ss.it keeps the windshied clear ,it comes on at a ceratin temp.that is what it said in the owners manual.i posted a question similar to yours.was recomended to leave it alone.not using any extra gas


#4

Drivers of many cars correct this “problem” themselves by modifying the switch. On some models it is as simple as slicing through an aluminum foil strip connecting two contact points. You need to find a specific Corolla forum and ask other Corolla owners how it is done.

Try this one: http://townhall-talk.edmunds.com/WebX/.ef14c39/?ed_displayMakeModelRelatedDiscussions!make=Toyota&model=Corolla at Edmunds TownHall.


#5

AC is key for defrosting in the winter. It removes moisture in car cabin that makes its way in. You are proving it to yourself by trying to put the setting on defrost but fan off(no AC) as it is far more ineffective than using low fan speed with the AC engaged.


#6

It will depend on where you live and when you drive, but around where I live, you really really want that A/C on with the defrost! In addition running the A/C from time to time during the winter helps keep things in good working order. Likely overall you will save money with it coming on by longer life of the compressor. The fuel cost of running that A/C is really very small.


#7

All modern systems that I’m familiar with do this. It’s to remove moisture. There are many circumstances such as melting ice off the windshield where it’s a detriment to achieving the goal.

I hate it when designers design that way. The problem with having systems do these things automatically is that they then compromise the situations where it is not the best option.

But I would not start modifying the system to avoid it. You do that at your own peril. As much as I hate it, I also recognize that it keeps the seals from dring up from lack of use.


#8

I agree with the others, the system was designed to work like that. Even my '82 has AC running with the heat (unless it’s in “econ” mode). Don’t worry about it.


#9

In cold weather the compressor won’t be running very much. Either there is a switch that keeps it shut off at low temps, or the pressure switch will keep it from running because there is little or nothing evaporating in the evaporator. The take-home message is, don’t worry about it unless you live in a desert environment.