PTC HTR ?

PTC heaters are "Positive Temperature Coefficient" heaters, and are 'assist' heaters used to heat the cabin. They come on when:

1) You select defrost, foot, or foot/defrost on the outlet control, and
2) The coolant and ambient temperatures are below a specific value.

Once the gas engine is warmed up, the PTC heaters turn off.


CHS stands for "Coolant Heat Storage", and is basically the radiator hot thermos system. So, I'm guessing W/P is "Water Pump"...

 

Wayne,

You get a gold star.

Even though I knew about the electric cabin heaters, I hadn't a clue about what the PTC abbreviation stood for, or CHS for that matter.

 

I won't lie, that one took some research!

 

Hey, you already scored a gold star by asking a hard-to-answer question on your very first post!

I don't know what the variables are to trigger those heaters, but you never know what tomorrow will bring...

Tell your friend not to be afraid to post, we only bite ocassionally. The best thing any brand-new poster can do is use the search feature before they post, but post anyway.

 

Did anyone come up with the environment variables at which the PTC is supposed to turn off? In Mine I think they pump out heat whenever in defrost or floor/defrost regardless of coolant or ambient temperature.

 

I can toss in a bit more info on PTC heaters. They are basically a conductive ceramic material that is basically a resistance heater, but their claim to fame is that they will self-regulate in that when the material heats to a critical temperature, the resistance goes up very quickly and thus acts as a built in "thermostat". First saw it used as the soleplate heater in a small clothes iron back when I worked in the small appliance electrical field a few years back.

 

From the service manual:

Apparently the 2 floor PTC heaters are 165 watts each and then the one in the Heater core is 500 watts. Toyota refers to this one as a "PS HTR", whatever that means. Add all of them up and that's a total of around 800w! Note this only pertains to model year 2006 and up. 2004-2005 only has the two 165 watt units, not the additional 500 watt PS HTR unit in the Heater Core.

There is another interesting note in the service manual:

This isn't surprising as if all 3 heaters are on they will be sucking down about 60 amps! Add the blower motor, lights, etc, and you would be way over what the DC-DC can provide.

 

I've attached a page out of the 2004 electrical wiring diagram manual. This shows basically the same circuit as can be found in the 2006 manual with three relays: PTC HTR1, PTC HTR2, and PS HTR. One heater has two heating elements and the other heater has one element.

One difference between the two model years is that the AC amplifier in the 2004 can choose to activate both of the two heating elements within the one heater, and/or the separate heater. In the 2006, the AC amplifier can choose to activate either or both heating elements within the one heater, and/or the separate heater. Hence the 2006 AC amplifier has a greater amount of heater control.

 

Strange, Although my manual says "preliminary", The description also only mentions 2 heaters. Maybe they changed mid year? Only in some markets?

I also noticed many ambiguities in the 2006 manual and incomplete descriptions.

 

I checked my 2004 and 2007, and they both have all three relays. Those relays live in the relay box mounted to the cowl, over the engine. The PS HTR relay is on the passenger side of the box, and is larger than the others.

I agree that the documentation is not perfect. I've attached a couple of pages out of the 2005 repair manual that omit mention of the PS HTR relay and the third heater.

 

So maybe they only outfitted them to certain markets? (Canada?)

 

Well, both of my Prius were sold by Servco Pacific (the Hawaii Toyota distributor) and Hawaii normally is not thought of as a cold weather locale - the low temp usually doesn't drop much below 65 degrees F.

 

Are the same ceramic heaters in the GenIII? I'm wondering what mine will be like with a PHEV kit in the cold.