Heat Pump: A/C Button Matter?

assuming 4gen is the same, the a/c button is air conditioning. even the the manual calls hvac, ac.

 

Thanks. When it's 15° outside and I turn on the heat/auto mode it always freaks me out to see the A/C light on. Too many years in "stooopid" cars.

 

The problem I’m having may be with terminology. In my mind A/C is for cooling, but it looks like Toyota considers cooling, or heating, as air conditioning (A/C)?

I have my car set to ECO, and air conditioning ECO modes. In humid 40 degree weather, I set the the system to a comfortable 65 degrees and AUTO mode. Seems to defog the windshield within a minute, and the car gets warm. The gas engine does not come on.

I’ve never pressed the button that looks like the standard defroster controller on other cars because I THINK that MAY allow the gas engine to start?

Don’t know, still learning & playing!

Craig

 

toyota calls a/c what we call hvac, heating, ventilation and air conditioning. technically, they are right. hvac conditions the air, cooling is one part, as is heating and etc.

 

To dehumidify air for the defroster, the heat pump needs to run in the cooling cycle; no heating is possible. That's why the ICE comes on normally with the defroster in cold temps. So what you propose could work as long as the temperature is set to lower than ambient. Note that while cold dry air will remove fogging, it won't work as well as warm dry air, and if the windshield is chilled, condensation can increase on either side.

 

The ICE coming on with defrost could be controlled by ambient temperature; under a certain temp it turns on no matter what the defrost temp is set too.

 

Then the ICE coming on might have nothing to do with the defroster at that time.

 

i thought the ice always comes on with the defroster.

 

I saw on one of the drawings of the Prime HVAC system that there is a both a condenser AND an evaporator inside the cabin, as well as an outside coil. How does the heat pump work in a Toyota Prius Prime plug-in hybrid? | PriusChat This allows one to get dehumidification without cooling the cabin and without requiring use of the ICE to reheat the air. It is way more complex than a typical home heat pump, which just reverses the flow of the refrigerant to reverse heat/cool roles. There is always hot, compressed refrigerant in the inside condenser, and cold refrigerant gas in the inside evaporator, and dampers control the air flow through them as appropriate. There is also a conventional ICE heating core inside the car with engine coolant. For ordinary dehumidification, the heat pump works fine, but when you need serious heat to defrost the windshield, that is when the ICE kicks in. There are no resistive heating elements in a Prime.

 

OK, so I want to get this straight. For heat, hopefully without the ICE turning on, and to dehumidify the interior, we need to turn on the A/C button on when using the heat pump heater? And without A/C button on, it won't dehumidify?

 

It’s unfortunate that the Owner’s Manual doesn’t really explain what the A/C switch does.

Toyota’s New Car Features book for the Prius Prime (available by subscription to techinfo.toyota.com), however, has an entire section (“Air Conditioning Control”) on this topic. It’s too much material to post here, but I can share two relevant quotes:

 

ScanGauge has a programable XGauge for ACWatts, can be used to monitor conclusively if the compressor is running or not. This is on 3rd gen, not sure if it also works on 4th and/or Prime.

My experience on a 2010 Canadian car:

The air conditioning compressor (old-school, american definition of AC) typically only runs when the AC button is pushed, it's light is on. The one exception: it will sometimes run when mode is set to Heat/Defog.

 

As an aside, I seemed to notice a faint vibration in the steering wheel when I called for heat this morning in EV mode, presumably from the Heat Pump running. Wondering if this is normal.