The Prius Has Multiple Heaters?

Yes, the Prius has two electrical resistance heaters that come into play when needed under cold conditions and high heat demands.

Tom

 

then they say A/C they mean Automatic Climate control.... there are various sensors in the car that check for humidity. turning on the A/C compressor draws the humidity out of the car... not that it stays on.. it doesn't, unless you want it to be cold in your car.. .which is represented by the number you choose on your autoclimate control.

 

Positive temperature coefficient - Wikipedia, the free encyclopedia

 

Someone reported the two electrical heaters are 400W each (from the Toyota Service manual). The 165W sounds like it may be correct, however, as I have only felt them once or twice, on cool mornings in late spring or early fall. They have no noticeable effect in winter here.

 

The circuits run from 30A fuses. That would suggest around 300W to me (they run from the 12V system) - if the current were much lower a smaller fuse should be fitted. 12V is nominal, of course; when charging the AUX battery, the actual voltage is closer to 14.4V, so they could be close on 400W.

The conditions for enabling the PTC heater are documented in the service manual. It says:

"The PTC heater is installed in the radiator in the heater unit on the driver and passenger’s FOOT sides and operates when cooling water temperature is low and normal heater effectiveness is insufficient. The air conditioner amplifier assy switches the circuit in the PTC relay and operates the PTC heater when the operating conditions (cooling water temperature is Below 55C (131F), setting temperature is MAX. HOT, air outlet damper position is FOOT or FOOT/DEF and blower switch in not OFF) are met".

(Preliminary service manual found at Index of /Documents_2004/ - see the 05 - Diagnostics zip file, ciha32.pdf under AIR CONDITIONING SYSTEM).

This preliminary manual also has a note in the Heater & Air Conditioner main document that says that they're only fitted in Cold Area Models. However, if the fuses are fitted (PTC HTR1 and PTC HTR2 in the junction box on the right-hand side of the engine bay) the heaters should be as well.

Given there are something like 24 steps from MAX COLD to MAX HOT on NHW20, most people can't be bothered to turn it all the way up with what seems like half a second between steps if you hold the button down.

The sequence goes MAX COLD - 16.0C - 16.5C - in 0.5C steps - 30C - MAX HOT.

So in theory, you could get more heat quickly, if you could be bothered to turn the heat all the way up - then turn it down again rapidly once it gets to the right temperature. With no easily-turnable knob, it's pretty much useless. (That m.f. display again!)

Edit: And straight away I find more/different information. The Air Conditioning System - Description document (dsc40001.pdf in the same folder) says:

When the hybrid system is operating (READY) and the blower motor is turned ON, the A/C amplifier (ECU) turns on the PTC heater if the conditions listed below are met.

Heater core integrated PTC Heater
Air outlet is in the FOOT, FOOT/DEF or DEF mode.
Engine coolant temperature is below specified temperature.
Ambient temperature is below specified temperature. (DEF mode)
Tentative air mix damper opening angle is above the specified value. (MAX HOT)

Footwell air duct integrated PTC heater
Air outlet is in the FOOT or FOOT/DEF mode.
Engine coolant temperature is below specified temperature.
Tentative air mix damper opening angle is above the specified value. (MAX HOT)

Yes, it turns out there's another PTC heater, and this one is directly at the driver's feet. This one is driven by the relay marked PS HTR, rather than either of the two PTC HTR relays, and is fused separately at 50A.

Looking at the conditions, they should come on when the coolant is cold and you specifically enable the blower - in this condition, in AUTO mode, the blower remains off. ("Warm–up Control: When the air outlet is in the FOOT, BI–LEVEL, or FOOT/DEF mode, the blower will not operate until the engine coolant temperature increases above a prescribed value.") It takes up to 30 seconds for them to come fully on.

Edit 2: After a cold few minutes sat outside in my cold car (0C currently at 11pm) I can say that either these instructions are wrong, my car doesn't have the PTC heaters (this is nearly as cold as it gets here), they don't work, or they don't work with the car in EV mode.

 

I have thought about wiring some LEDs to the PTC elements just as a way to see when they really do turn on. There is a wire labeled IDH that signals from the DC/DC converter to the climate control so that when the total electrical load on the converter is high enough, the PTC heat can be inhibited. I have a suspicion that the real control rule is something simpler than the manual makes out (say, something about temperature, coolant temp, and not-IDH) and the manual is just trying to give a bunch of conditions you can easily replicate to be sure you've satisfied the rule when you want to test the heaters, since there's no direct view or control of the IDH signal. But I haven't experimented with it.

-Chap

 

Hi All,

The electric heaters are noticable when you get defogging on a cold morning, as soon as you start driving. Its difficult for a human hand to notice their heat output, as the fan needs to be on for them to enabled, I guess. And so the cooling effect of the air flow reduces the warmth you would feel. But, blowing a cold unheated stream of air on a fogged over window does very little. But the defogger readly clears up the glass when the car has been on for only a minute or two.

 

That is much more likely due to the compressor removing moisture / humidity than any ceramic heating of air.

 

With only 165 watts of output it would be like trying to feel the heat of a 100 watt light globe from a foot away with a small desk fan behind the globe. I think it just lifts the temperature a little to help defrost the windows quicker.