Anyway to turn off the compressor (A/C) ?

In every vehicle I have owned in the past 20+ years, the A/C automatically comes on when one engages the DEFROST. This is deliberate in that the cooling action of the A/C removes moistures from the air stream.
.. but then maybe you prefer a steamy windshield.

 

As Teakwood says this has been common practice for a long time because if you're directing air towards the windshield the assumption is that you want it to be defrosted. Rather than a firmware update the simple solution would be to not direct the air at the windshield.

 

The Gen II Prius has an "A/C" soft button that enables the A/C compressor. I'm surprised that the Gen III lacks this feature. Are you sure that it is missing?

Tom

 

I'm in OC, and have been turning off the AC because it's colder outside - but this brings in cold wet air, which as you see fogs up everything. I found *if* you leave it in defrost (no AC), and blow it good - it keeps the car fog free - but I then found that I really didn't care - so I pressed that AC ON button - and no longer did I have any issues with fog (air recirc, or from outside)...

 

All my Toyota cars are like that. I would prefer more control, but more typical driver probably likes simple solutions. I do auto climate (set to 65) and only use defrost when needed. Works for me.

 

Uh, guys, there is a humidity sensor in the system. If the humidity is low enough the compressor will stop. If the humidity is high enough it will run. If the humidity is high enough you WANT it to run. Unless you'd rather not see where you're going!

 

How can you tell when AC works? I cannot hear a difference over engine noise.

 

Thanks, I didn't know the A/C was well-integrated into the windshield-defrosting system; I had wondered about that. It's a feature, not a bug. Any mileage hit is truly small potatoes, since no one leaves defrost on when it's not needed. #7 also noted the humidity sensor, another good thing to know.

 

Only way I've found is to monitor the air outlet temp. I've used an inexpensive indoor/outdoor thermometer (electronic) with the outside sensor dangling in a vent. Now I admit, at -18C ambient (0F), starting the cold car, it's kind of difficult to notice! But once it starts to warm up you can see it cycle.

 

Tom,

Maybe it's too much coquito, (Hispanic egg nog) I don't understand.
Could you explain what this means in the Gen II?

 

There's an A/C button on gen III. If you've got the ventilation Mode set to Heat/Defog, or have hit the front windshield defog button, then regardless of the A/C button being off (unlit) or on (lit), then A/C likely is running?

 

Remembering that in Prius speak "A/C" means literally conditioning of the air, that is heating or cooling, when it's on the compressor could be running. It runs when the humidity is high enough. Note that cold air is "more humid" with less water vapour in it, so you'll find it running more when it's cold. It runs to de-humidify the air.
Also note that in the Prius having the compressor running has a much lower effect on mileage/power than in obsolete cars.

 

By "soft button" I mean a virtual button on the touch screen. It's on the climate page, down on the lower left corner.

I believe the Gen III has a physical button on the climate control section of the dash.

Tom

 

What makes me laugh is when I see cars with the windows totally fogged; I just want to lean over and switch from 'recirc' to 'vent.'

 

My 2004 Prius had a A/C soft button on the HVAC page to disable the A/C

My '07 FJ will automatically run the A/C compressor when the selector knob is in defrost or the blend setting floor/defrost.

Since I have heated parking, that means when I pull away at -40, the A/C will run until the LP switch trips and disables the compressor. That means cold air from the defrost until the A/C trips out

Note: an automotive A/C can NOT run in temps much below freezing without damage. Hence the LP and HP trip switches on the LP and HP lines of the A/C system

With the FJ, there is no way to disable the A/C from running in defrost. So I consulted the service manual and found an easy solution:

pull the clutch relay

Problem solved. The A/C indicator on the dash blinks to indicate a fault, but all you have to do is poke the A/C button again to cancel the warning and return the idle speed to normal

 

You could always disconnect the compressor eletrical wire from the compressor if it really brothers people.



Not a good idea, since I am sure the computer will notice that and give you a error on the dash.

 

They run the compressor to dry the air in defrost mode. It makes the defroster much more effective at defogging.

The load on the compressor (power required) is not constant. It varies with compressor speed (which the Prius can control, unlike conventional systems) and largely by discharge pressure (which is very low on a cool/cold day).

Running the compressor on low in cool weather actually takes very little power, nowhere near as much as on high during summer.

Just let it do it's job on defrost.