The ptc heater

Discussion in 'Gen 2 Prius Technical Discussion' started by Oddest_raindrop, Jan 2, 2010.

  1. Oddest_raindrop

    Oddest_raindrop New Member

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    For a while now I have been wondering what does it take to turn this thing on. I read the forums here and one thing seemed clear. I needed more info. I decided to do some testing on my own.
    I got a device called a fuse buddy. You can pull out an existing fuse and install it in this tester then put it in the place where the fuse was. It will measure the current that runs through this fuse. I decided to hook it up to each of the ptc fuses in the engine compartment.
    After starting I played with the heater controls.
    With the heater set to foot or foot and defrost the heaters do kick in and work. They did this with any heat setting but max low. Also if the auto setting had the foot and def on and the fan running it would turn the heaters on. I tested this with engine temp up to 136 and they stayed on. Not sure how far it would have to go to get them to come off since I had the hood up and wasn't about to drive it.
    The current draw started at 16 amps and quickly droped to around 14 amps, with it eventually settling at 13.5 at this time I measure the 12V voltage with the scanguage it was at 13.7 equaling a working 184 watts this was roughly the same for both heater circuits that were fused at 30 amps. This gives us 368 watts of heat provided. While doing this the outside temp as displayed at 28 F on the MFD.
    I hope this give light to anyone that was wondering about these heaters as I was for the past couple years.
     
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  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Nice work.

    So the two PTC heaters are equivalent to 25% of a 1,500 watt hair dryer. No wonder it takes a while for the heat to appear in cold weather...
     
  3. efusco

    efusco Moderator Emeritus
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    Agree, very nice work, the first time I've seen anyone take a serious look at how/when they work and actual energy consumption vs output.
     
  4. BAllanJ

    BAllanJ Active Member

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    So I'm guessing at this power level they're only intended to keep your breath from fogging the windshield while waiting for the serious heat to come from the ice a few miles down the road. They can't be thinking that this'll warm the cabin much.
     
  5. efusco

    efusco Moderator Emeritus
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    Exactly, something to keep the incoming air from being completely frigid, but no way low wattage heaters like that will bring significant warmth.
     
  6. peirhead

    peirhead Junior Member

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    I prefer to use my AC in the floor/defrost mode but it seems that the little heaters are on even when it is the 80s...Is there a programming option to set this feature only when the auto temp control is calling for heat?
     
  7. pEEf

    pEEf Engineer - EV nut

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    I suspect the PTC comes on in Defrost mode because the goal is removing humidity, while maintaining the temperature. Without the extra heat the AC would cool while trying to dehumidify.
     
  8. astrand

    astrand PHEV Guru

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    This is what the repair manual says:

    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).

    Note that "MAX HOT" can mean two different things. It can mean the highest temperature setting (also called Max. Warm sometimes), OR it can mean the position of the Air Mix Damper. But the text above is of course pretty clear.

    The position of the Air Mix Damper should basically correspond to the current temp setting and the current cabin temp. So, if it's colder in the cabin than what you have asked for, the Air Mix Damper is probably at MAX HOT.

    The repair manual is a little bit confusing: It says that when testing the system, you should set Temperature: Max. HOT, Ventilator Mode: FOOT, and initially Blower switch: OFF. But in my car, this turns off the entire AC system, and the PTCs goes off. I need to use "AUTO" for the PTCs to come on.

    The manual says that changing the blower to LO cancels the PTCs, and I've confirmed this. I don't understand why they have designed it this way.
     
  9. astrand

    astrand PHEV Guru

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    My problem is the opposite: The PTCs are turned off way too early, initial tests indicates that they are turned off when the engine temp is about 40 degrees celsius or so. I'm planning a mod that basically runs the PTCs all the time, at least during the cold season. I might need to cancel the PTCs when the electrical load on the vehicle is high, just like the AC ECU does, but I wonder how this can be done...
     
  10. peirhead

    peirhead Junior Member

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    Which are the PTC fuses in the Gen3.....Can I remove them to disable just the PTC heaters, or are they part of a larger component set?

    I always use floor or defrost in combination with the vents for air conditioning and it seems the PTC heaters are ALWAYS ON regardless of engine and outside temperatures.
     
  11. AzWxGuy

    AzWxGuy Weather Guy

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    I've been wondering about this myself, as it seems the heaters are activated even when the climate control system is set to OFF. I notice this on cool mornings driving to work, maybe low 50's outside with tolerable inside temperatures. I have climate control off and recirculate set to outside vent. To turn them off I have to set a fan speed, manually roll the temperature to LO, then turn it back off again. I guess OFF really isn't OFF.
     
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  12. nh7o

    nh7o Off grid since 1980

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    Interesting. This might be a factor in the various posts from people trying to determine the reason for their unexplained MPG drops. The fuse buddy looks to be worthy tool in this situation.
     
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