Disabling the compressor when using defrost on a Toyota Corolla
 

For all you Rolla owners.
Been looking to do this and found these directions.

http://www.greenmycon.com/Resources/..._Defroster.pdf

I'll have to see if I can do this with my Matrix... Thanks.

Just so you guys are aware, the reason that the units are coupled is the A/C is never used during the winter, but the defroster is. The compressor will seize up if not used periodically, so the simplest solution to the problem of seizing was to have it run during the winter as well as the summer.

If you do this mod, make sure to run your A/C three or four times during the winter for about 3 minutes (no longer than that otherwise the system will freeze, it is recommended not to use the A/C below 60F because of that reason), because your defroster won't do it for you anymore.

Other than that good mod, I would like to see the MPG gain from this one.

That's a myth. There is no reason why a compressor has to be used to keep it working. They easily sit unused for years in supply houses and work just fine when installed. In fact, operating a compressor without a crankcase heater when cold can cause valve damage from liquid refrigerant collecting in the cylinders.

The myth probably originated from the old days when the capacitors used with compressors would lose the dielectric layer when left unused. That results in catastrophic failure when it is later operated. However, modern capacitors don't have that problem, certainly not within a year.

I have done this to other cars in the past, more for performance reasons then FE reasons, but I have never had a problem with the AC or with defrosting.

The sole reason for turning on the ac compressor when the defroster is on is to dehumidify the air blowing on the windshield to prevent it from fogging up.

Hi,

I want to do this mod in my xA. When driving in an ice storm, you need the defrost to be as hot as possible. If I need the quick defogging action, I'll turn on the A/C manually; thank you very much.

Running the A/C ruins my gas mileage.

Just remove the compressor fuse for the winter and reinstall it for the summer if you don't have the time to modify the controls. Another solution might be to install a thermal switch in series with the contactor coil so it will not turn on when it's cold.

Thanks for that,

I'll have to look for the fuse -- it would disable the clutch that engages the compressor; since the compressor is mechanically driven, right?

If I could disable it on the switch, then I could still manually run the A/C, if needed.

If you remove the fuse, the compressor will simply not power on when the contactor is closed. The fuse is in series with the compressor contactor so in effect, the circuit will behave as if the contactor has not closed.