Is this normal ? ? ? (AC Compressor/Radiator Fan)

[mareakin]

I've noticed that the radiator fan turns on for 5 seconds, then turns off for 5 seconds, then repeat every five seconds whenever the DEFROSTER is on--even when the temperature dial is set to maximum-HOT.

Whenever the radiator fan turns on, I notice the engine idle speed (normally, 800 rpm) spike to 1100rpm, then when the fan turns off--800 rpm again.

I'm going to assume that when the engine idle speed spikes, the AC compressor is actually engaging.

Isn't this ODD? I think so, for two reasons:

1. WHY would the radiator fan & AC Compressor need to be ON when I'm using the defroster on an ICY cold day, when the temperature dial is set to MAX-hot??

2. WHY does this happen ON&OFF, ON&OFF, every five seconds??


Car: 2007 Corolla, 43,000 miles. Everything STOCK.

 

[mareakin]

My understanding is that FROSTING occurs on the window because of heat difference between inside and outside of the car.

I can understand the AC Compressor coming into play on a humid or HOT day (to blow cold air on the window to get rid of the frost)

But on a REALLY COLD ICY Day, why does it need to be on? Plus, I've already set the temperature to MAX-HOT.

Doesn't make sense.

I'm going to assume this is an ECU problem.

 

[punisher]

Normal operation.

On very cold days the evap pressure is low to begin with, and the compressor will only cycle for a few seconds until the cycle switch cuts out. The AC is on by default when defrost is selected regardless of temps.

It has nothing to do with your temp selection.

 

[Axe Man]

This is completely normal. My Civic does the same. And most other
vehicles do too.

The A/C compressor is cycled during defrost operation to dehumidify the cabin.

 

[The_Jeff]

Any colder and the AC won't cycle at all. If they engineered the car better they'd have elminiated it at the temp you suffered because as you said its annoying.

If you look around your AC lines there's a pressure switch you can disconnect all winter... disabling the system and saving gas.

 

[mechanicx]

Yep that's the nature of cycling clutch A/C systems. And the A/C compressor is activated when the Defrost mode if the temperature is above around 40 degrees. I do think GM's variable displacement control valve is a better way without cycling the compressor.

 

[mechtech2]

This is normal. 'More' normal on some cars!
The mfrs. want that compressor on in the winter here and there to keep the main seal on the compressor lubed,and keep the parts free internally.
They usually make the AC go on when the defrosters are on to accomplish this. Often at other heater/vent settings - it varies car to car.

 

[artificialist]

The A/C causes condensation to leave the air, and that aids in removing the fog from the windows.

And it is said to be normal on cycling clutch systems? The Toyota Corolla uses a thermostatic expansion valve.

 

[demarpaint]

Originally Posted By: mareakin

Whenever the radiator fan turns on, I notice the engine idle speed (normally, 800 rpm) spike to 1100rpm, then when the fan turns off--800 rpm again.




That spike in rpms becomes even more annoying if you are driving a stick and trying to take off when the compressor decides to kick in. Every 5 seconds is a royal PIA! Very annoying!