Yet another heat question.

Discussion in 'General Automotive Tech' started by zzzizxz, Jan 5, 2018.

  1. zzzizxz

    zzzizxz Well-Known Member

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    Hi all,

    I've looked through all the posts on here I can find that talk about issues with heat, and I cannot find anything that helps me.

    My issue is that my heat isn't all that hot in mt 1981 Pontiac Safari

    And now, here is the back story.

    Engine was completely rebuilt one year ago by a reputable garage.
    In August, the auto climate control wiring burned up.
    Same garage replaced the Auto controls with manual controls.
    When it got cold here about a month ago, I realized that I had good heat coming out of the vents if the fan was on the lowest two settings, but as soon as I turned the fan up to the faster settings, I only got cool/cold air.

    First thing I checked was that the cable to the hot/cold door was connected and was working correctly. (It is)

    Based on this information, I figured it was a partially clogged/blocked heater core.

    Took it back to the same garage, where they replaced the heater core, as well as the heater control valve.

    Now, I have better heat than before, but not by much. After letting the car idle for ~15 minutes, and city driving for 20 minutes, I only have cool air on the economy heat/vent setting.
    On defrost setting, at WOT, I get about 112 degrees out of the vent. As soon as I'm at idle, it is back to cool.

    Here are the temperatures I measured. Everything is in Fahrenheit.

    At idle
    hose into the heater core reads ~135
    Hose coming out reads ~95

    On defrost setting at idle
    Fan high - 92*
    High med - 102*
    med - 110*
    Low 127*

    On defrost at WOT
    High - 119*
    H med - 129*
    Med - 135*
    Low - 140*

    Heater set to vent at idle
    High - 81*
    H med - 85*
    Med - 90*
    Low - 92*

    Vent at WOT
    High - 98*
    H med - 99*
    Med - 100*
    Low - 99*


    Outside air here is around 5F.

    Can anyone offer any suggestions as to what the issue is, or to what needs to be fixed/adjusted??

    Did I get a faulty heater core??

    Thank you!
     
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  2. Silvertwinkiehobo

    Silvertwinkiehobo "Everything that breaks starts with 'F.'"

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    It's telling that the DEF is where it just about should be (bear in mind, cold is gonna suck heat out of the radiator, so not much is left over for the heater) but all the other settings have reduced heat. It sounds like something in the controls is 'catching,' that ends up changing the blend controls, so you end up with less heat. You need to see if you can verify where the temp blend door actually ends up at in each major setting with the temp set fully hot. Start with that, and just remember that the fan pulls in unheated air to move through the system, but that should not mean major temperature reduction.
     
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  3. ross

    ross Well-Known Member

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    What is the coolant temp?
    Seems like overcooling to me, not hard to imagine at 5*ambient if the stat is opening too low.
    Could also be air leaking from the ducts, these weren't exactly precision fit when new and if the dash has been aprt for repair...........
     
  4. zzzizxz

    zzzizxz Well-Known Member

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    I want to make sure I know what you mean here, so bear with me. When you say "Temp Blend Door", do you mean the little door behind the glove compartment that is supposed to be closed when the temperature selector knob is set to "heat", and open when the knob is set to "cold"?

    If so, that door has been converted to manual function, and it does not move when I change the fan speed. When I put it to "hot" it is fully closed.

    I do understand that the heat won't be as "hot" when it is 5* as when it is 30*, but I would like to know if there is something that needs fixed or adjusted in this system. As it sits now, I do not get a warm car when I'm driving around, unless I am driving at highway speeds for more than 30 minutes. Which seems a little unreasonable to me.
     
  5. zzzizxz

    zzzizxz Well-Known Member

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    Not positive if the temp gauge in the dash is 100% accurate, but it states that the coolant temp is about 230 normal running operation.
     
  6. 63Fowagon

    63Fowagon Well-Known Member

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    Sounds like you are getting outside air through a/c still that would explain lower temps on high fan thus sucking more fresh air through a/c . Don't know your system but another door needs to close . A/c units cycle both inside air and outside air depending on setting .
     
  7. Silvertwinkiehobo

    Silvertwinkiehobo "Everything that breaks starts with 'F.'"

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    Yes. And what I was angling at, is whether changing the mode selector, from DEF to DEF/HEAT, to HEAT, etc., is causing the temp blend door to physically move, an unwanted movement.
    Also, I don't think RECIRC is part of it, based on the fact that it is locked to FRESH when the DEF is set, whether DEF or DEF/HEAT. It has the proper temp on DEF, but not on DEF/HEAT. The position of the RECIRC door would not cause that.
     
  8. Krash Kadillak

    Krash Kadillak Well-Known Member

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    I've had similar troubles with my system, Z, which was the same as yours. In my opinion, it's a troubling system, even when working correctly.

    With your replaced control unit, there's no telling where the issue is. You need some kind of Auto HVAC system expert......
    I think checking the thermostat would be the first thing I would do.

    I had my heater core replaced a few months back......
    - 'Defrost' setting seems to work OK
    - 'Bi-Level' setting seems to get the most comfortable temps, but I can't get it push more air out - the fan speed seems to only respond when I have it in the 'A/C' mode. There, I can select Lo, Medium or High.
    - 'Economy' - not sure when the right time is to use this setting.....?
    - I'm even getting some heat from the system when it's set to 'Off'.....
     
  9. Silvertwinkiehobo

    Silvertwinkiehobo "Everything that breaks starts with 'F.'"

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    If the system doesn't have an underhood control valve, then hot coolant will always circulate. You could, if you don't mind modding your wagon, get a Jeep or other maker's hot water control valve. I suggest the Jeep ones because when the valve is closed, the coolant is looped back, as it has four nipples and is spliced in to the hoses. Controlling it is the problem--you need vacuum to hold it in one position, whether it's open or closed.
     

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