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Thread: Heater Control Valve temporary bypass

  1. #1
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    Heater Control Valve temporary bypass

    Quick question, im trying to get my car re assembled for a Car Show this weekend and I cannot find the Heater Control Valve,
    Im guessing it got tossed out at some point. If I assemble the heater line without it, will my ac still blow cold? Ive got a new one on order but it won't be here
    in time for the show.
    Thanks.

  2. #2
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    Quote Originally Posted by rustycarr View Post
    Quick question, im trying to get my car re assembled for a Car Show this weekend and I cannot find the Heater Control Valve,
    Im guessing it got tossed out at some point. If I assemble the heater line without it, will my ac still blow cold? Ive got a new one on order but it won't be here
    in time for the show.
    Thanks.
    Simple answer. No it's not going to be cold. Just connect the hoses at the engine until your ready to put the heater core in the loop. This is a very common thing to do.




    Dave B.

  3. #3
    Senior Member Bitsyncmaster's Avatar
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    It would not be as cold on MAX AC but would be the same on normal AC.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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    Thanks

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    LS Swapper Josh's Avatar
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  6. #6
    absotively posilutely bytes311's Avatar
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    Quote Originally Posted by WHO1DMC View Post
    Simple answer. No it's not going to be cold. Just connect the hoses at the engine until your ready to put the heater core in the loop. This is a very common thing to do.




    Dave B.
    I've come across this topic before but haven't been able to find a clear explanation. How exactly does the heater core influence the AC's cold air output? Aren't the two systems separate and independent? I'm genuinely curious.

  7. #7
    Senior Member r00b's Avatar
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    Quote Originally Posted by rustycarr View Post
    Ive got a new one on order
    Thanks.
    I hope you didn't order it from DMCH? I went threw 3 of them before I learned that DMCH just sells junk.
    When I did my frame off I looked for something better, I found a metal one for a 1976-1996 Jaguar XJS.

    20191122_161449.jpg
    20191122_161456.jpg

    Having changed out the garbage plastic ones so many times, I decided to relocate it to make it easier to change out. It's been in there now for about 5 years and I haven't had a problem with it. I did have to lengthen the vacuum line.

  8. #8
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    Quote Originally Posted by bytes311 View Post
    I've come across this topic before but haven't been able to find a clear explanation. How exactly does the heater core influence the AC's cold air output? Aren't the two systems separate and independent? I'm genuinely curious.
    The heater core and the A/C evaporator are installed in the box and are "separated" by a mixture paddle. As you turn the Hot/Cold dial, that dial is connected to a cable that pulls/pushes the paddle so that it can properly mix the cold and hot air to coincide with where you set that temp dial.

    The only time the heater valve is closed off is when you have the dial set to Max A/C, by cutting off the heater core from receiving hot coolant, you get the coldest air possible from your A/C. When in normal A/C mode, the heater valve is open allowing hot coolant to travel through the heater core, this allows you to set the temp slightly warmer with the A/C on.

    If you splice the line together to eliminate the heater valve temporarily, you'll still have A/C, but it will always run in Normal A/C mode (when you turn the A/C on only) even if you set it to Max A/C. Just make sure you either cap the vacuum line that is supposed to go to the heater valve or take care to not set it to Max A/C as you may create a vacuum leak.

  9. #9
    absotively posilutely bytes311's Avatar
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    Quote Originally Posted by dmcman73 View Post
    The heater core and the A/C evaporator are installed in the box and are "separated" by a mixture paddle. As you turn the Hot/Cold dial, that dial is connected to a cable that pulls/pushes the paddle so that it can properly mix the cold and hot air to coincide with where you set that temp dial.

    The only time the heater valve is closed off is when you have the dial set to Max A/C, by cutting off the heater core from receiving hot coolant, you get the coldest air possible from your A/C. When in normal A/C mode, the heater valve is open allowing hot coolant to travel through the heater core, this allows you to set the temp slightly warmer with the A/C on.

    If you splice the line together to eliminate the heater valve temporarily, you'll still have A/C, but it will always run in Normal A/C mode (when you turn the A/C on only) even if you set it to Max A/C. Just make sure you either cap the vacuum line that is supposed to go to the heater valve or take care to not set it to Max A/C as you may create a vacuum leak.
    Thank you! That makes sense now. I forgot that we have a temperature dial with a range from hot to cold, which I never use. I always set it to one extreme or the other.

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