Turning on and off defrost turns on heater

The Prius is designed with automatic climate control. In normal use you set a temperature and then forget about it. If you are cold, bump up the setting. If you are warm, lower the temperature setting. You can do it right from the steering wheel. Trying to manually override the automatic system just makes a lot of work for you. Even on manual, the temperature setpoint is used to determine heat output.

If you insist, you can use the Auto A/C button on the steering wheel to cancel automatic mode. I don't know of any way to change the default behavior when switching to defrost. There may be a way, but not to my knowledge.

Tom

 

I noticed the same thing on my 2007 yesterday. I started with the heater off to get the engine temp up as fast as possible, turned on the defroster for 30 seconds or so and when I got to a red light a bit later noticed that the fan was running.

Seeing how fast the heater can lower the water temp was a real eye-opener - even more than seeing how much current is generated under modest braking while at highway speeds.

 

This is a major pet peeve of mine about the car. I have brought it up here on the forum before (with little to no empathy from others). Glad to know it bothers someone else as well.

Its most bothersome now during the winter with my very short commute. I hate having to deal with the car going into Auto A/C whenever I need a few seconds of defrosting.

The only alternative is to start the defrost and then turn the Auto A/C off in the climate control screen of the MFD. However, with the defrost left on (even at a low hear setting) that still results in the ICE running at stop lights till it warms up (which given my short drive will never occur). So I'm left with having to hit two buttons on the steering wheel (one on each side just to increase the pain) to turn the defrost (and the heater) back off.

An annoyance... some might say befitting the driver

 

That's why I gave up fighting the car. I tried that sort of approach when my Prius was new, and soon realized that it's easier to let it do its thing. The only climate buttons I use are the ones setting the temperature and the defrost button. Otherwise I leave everything on automatic.

I know it should be easier, but it isn't. From my perspective the small potential gain isn't worth the effort.

Tom

 

Hi All,

I have been using this "feature" to get the engine down to about 85C, when it gets up to 90C in my drive home. As I have a 90 % grill block on the car right now. In the morning, its 15 F and its just not a problem. But some of the evening commute temps are up to 35 F lately. So, with the add-on temp gauge I know when to trigger the heater that way without taking my eyes off the road. Then when I roll into a stop, I do the Climate/Off buttons.

 

I think this may be one of the dealer-settable options. There are a number of such settings, such as "is the A/C enable turned on when you press the AUTO A/C button (default yes)".

Ah, found a copy of the relevant page: http://andrew.daviel.org/prius/m_01_0030.pdf

No, there's no such setting. You should be able to just press the AUTO A/C to shut the climate control off though, rather than going to the climate screen.

 

The 4th one down the list of AC options in the document you provided may in fact set something close to what I want. It appear the default for the defrost button is to be "linked" with A/C ON by default. This linking seems to be one way - turning defrost on when A/C OFF turns the A/C ON as well (assuming it was off) but does not turn A/C OFF when you turn the defroster back off. There seems to be a "normal" mode option where maybe they are not linked at all.

So I need to ask the dealer to change this. I assume it requires special equipment to change?

 

I wanted to chime in here, because I am becoming disillusioned with my car this winter. My commute is about 12 miles, mostly at 35 mph with no stops. After the 15-20 minutes of driving my coolant is still not warm enough to go into full hybrid mode, only about 64 degrees C, the windshield is still frosted inside and most of the ice is still unmelted on the outside. I'm scraping the inside of my windshield for the first time since owning a 1965 beetle. I've tried setting the temperature to the very first notch above LO, 18 degrees Celsius to get a bit of heat, but hopefully have the engine warm up as quickly as possible.
I have pipe insulation in the grill and I use a block heater which seems to do nothing to help the problem. The last car that did this was quickly fixed by changing the water thermostat. My dealer had the car yesterday and scanned the system before telling me the thermostat is fine. So I'm left with a car that can't generate enough heat in the engine to reach operating temperature, and if I choose to try and make the cabin liveable, the engine loses even more heat...it's really dramatic, and the temperature is just -15 degrees C, or five degrees F. What do the folks in Wisconsin and Alberta do in their Prii to survive? This is my first complaint about the car, and I seem to be destined to be frustrated for another couple of months. Any suggestions or agreement on this problem from cold-weather owners?

 

The key with your situation is to stop fooling around and let the climate control do its job. Set it on A/C Auto, set the temperature where you want it, and press Defrost if the windshield starts to fog or freeze. It does a good job if you let it. If you try to second guess it for optimization, you are going to have the kind of problems you describe.

A block heater helps too. If I had your drive, I might use one.

Tom

 

I do have the block heater, and the water temp is no higher at points along the commute than without using the BH. In retrospect, it was a waste of money. I actually have tried to let the heating system do its thing at one set temp...the engine takes 15 to 20 minutes to reach a tepid 62 or 64 degrees with the cabin heat on. Operating temp is supposed to be 83 degrees.

I've tried leaving the heating system on LO, not taking any heat away from the engine to heat the cabin, and the car manages to reach 74 at the same point along my route. I'm frozen and the windows are frosted. Considering all, I prefer to sacrifice some gas for warmth, but I expect the heat to rise faster, and have heat before I reach work.

It just seems that the coolant flow to the rad is unrestricted, and the heater core adds more rad surface than the engine can produce heat for in my car. I don't remember this problem last winter, but the dealer insists the car checks out fine.

The heat capture system designed in the 2010 will be a welcomed addition.

 

I think that refers to the A/C compressor - ie the A/C enable on the screen, rather than the (misnamed) "A/C AUTO" . But I've no first-hand experience - it could do what you want.

I think they do it using their normal diagnostic tool. I don't think those settings can be changed without that.

 

Hmm, I'd try diagnosis at another dealer. The engine ought to heat up faster than that. The fact that you recall no such problem last winter is certainly suggestive of a problem.

Just curious: how is it that you have a 12 mile drive at 35 MPH with few stops? is it on a twisty country road, or what?

 

I drive along a scenic street that follows Lake St. Clair (the forgotten Great Lake) and the Detroit river. There are only six stop lights, visible for long distances to adjust speed and avoid the reds, and zero changes in elevation. In warmer weather I have to pull over when the engine temp hits 70C to put the car in full hybrid mode, but certainly not now.
The nearest alternative dealer is unfortunately 50 miles away. If it continues to be a problem I'll take it back and get the coolant thermostat changed off-warranty because that's all I can think of the problem being.

 

Do you have the top & bottom grill blocked off with pipe foam? Makes a big diff. for me.

 

I have pipe insulation in my grill for the second winter. No problems last year with frost or low engine temps.
I included some shots of my scangauge and windshield after a 25 minute drive home. Note the frost on the inside of the glass, and scraper marks in it. The engine temp with the engine still running and the defrost on maximum is still just a tepid 51 degrees C, 32 degrees below operating temp.
I am kind of railing on this issue. BTW, I'm a huge Prius fan, and this is my first disappointment. If it's normal engine performance for the car in weather as cold as we've had this year, so be it. But the dealer says the engine is behaving as expected. I'm mistaken. I was hoping somebody could tell me this is their experience north of the 42nd parallel, and I should live with it, and never drive far with kids in the back seat in winter.

 

every car, imo, should have 4 separate climate areas.

1) A/C on or off

2) temperature (i prefer blue to red, since the temp. numbers are usually meaningless)

3) fan speed

4) which vents are open


i don't mind automatic feature, but make it an OPTION. i hate that if i want to change the passive temp in the prius, i have to turn on the fan, then select the temp, then turn off the fan. SOOO dumb.

 

Wow! You need to get that thing back to the dealer. There is no way you should see that sort of ice buildup on the interior. It seems like maybe your AC condenser and/or compressor is malfunctioning and not stripping humidity from the cabin air. This is a key feature to modern defrost units. Also, I live well north of the 42nd parallel, and I don't have any issues. I'll admit that the heater is not as good as a conventionally driven care with a larger ICE, but it works fairly well even at -20F. I don't have a block heater, but my car is garaged overnight. My wife and I carpool and drop our four month old daughter at daycare without any issues. She is in a car seat with a blanket over her. I have sat in the backseat with her, and I can honestly say that, while not 70F, it was certainly comfortable.

Our technique in the winter is to block the entire upper and lower grill with pipe insulation. We tend to set the climate control on AC auto to 70F and apply the defrost as needed. I have never experienced ice building up on the inside of the windshield, though from experience with previous cars, this is often indicative of a poorly functioning AC compressor, leaking heater core, or both. I would get thee back to the dealership. Hope this helps.

 

I just noticed in my 2006 that the A/C compressor was turning on when the defrost button is pressed and the A/C button was or was not pressed whether there was the A/C button indicating being on or off.

I noticed after doing some tune up work and listening a little more than I guess I have in the past. Was thinking was an issue with the Digitizer Screen at first, though using the steering wheel button to turn on and off A/C did nothing to start or stop the compressor. Only turning off the Defrost only or Defrost with Floor ventilation turned off the A/C compressor.

Reading the above makes more sense now. Just doesn't seem the most energy efficient and though maybe is using a refrigeration cycle. Also, seems like can wear the A/C compressor if temp or humidity sensor(s) was/were bad maybe?