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Thread: Heater control valve not getting vacuum?

  1. #1
    EFI Guy
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    Heater control valve not getting vacuum?

    My A/C, while it is cold, isn't as cold as it can be - I get ~55 out of the vents, not ~40. This has been going on since last summer. Yes, I have put the A/C gauges on, and everything checks out there.

    I noticed that when put on the max setting, that the heater control valve in the engine bay wasn't pulling its flap shut. I thought that maybe this was because of my A/C mode switch diaphragm, which I have heard hissing for as long as I can remember.

    So I changed the diaphragm out yesterday. That made no change in the operation of the heater control valve. I pulled the vacuum line out of the heater control valve, and found that it isn't pulling vacuum.

    Not sure how to proceed from here.
    -Mike
    2005 Lotus Elise, chrome orange, naked carbon fiber front clam, baffled oil pan, rear toe link brace
    1987 Lotus Esprit Turbo HCi
    1999 Saturn SL1, running like a champ
    1981 DMC DeLorean, Alpine head unit + Genesis P5 amplifier + subwoofer, Eibach springs + Houston Shocks, EFI via MS2Extra & Renault Z7U intake manifold, self-installed DPI Spec 2 engine package

  2. #2
    Quietly enjoying ownership Cory W's Avatar
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    Were you been in the center console around that time? Any vacuum hoses pull off there? Maybe rearranged at the mode switch somehow? Check all junctions as well back there, since it's not impossible for them to come off at that point.

  3. #3
    EFI Guy
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    Nope, hadn't been in the console around the time the control valve stopped, um, controlling.

    From my experience replacing the diaphragm the other day, you aren't kidding; super easy to knock things loose back there!
    -Mike
    2005 Lotus Elise, chrome orange, naked carbon fiber front clam, baffled oil pan, rear toe link brace
    1987 Lotus Esprit Turbo HCi
    1999 Saturn SL1, running like a champ
    1981 DMC DeLorean, Alpine head unit + Genesis P5 amplifier + subwoofer, Eibach springs + Houston Shocks, EFI via MS2Extra & Renault Z7U intake manifold, self-installed DPI Spec 2 engine package

  4. #4
    Quietly enjoying ownership Cory W's Avatar
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    Quote Originally Posted by opethmike View Post
    Nope, hadn't been in the console around the time the control valve stopped, um, controlling.

    From my experience replacing the diaphragm the other day, you aren't kidding; super easy to knock things loose back there!
    The line that isn't pulling vacuum, have you followed it backwards? You never know if you may find a leak, or a line disconnected further back Nothing is impossible; you could even find a clog in a line? Maybe a line got pinched somewhere...

  5. #5
    EFI Guy
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    Quote Originally Posted by Cory W View Post
    The line that isn't pulling vacuum, have you followed it backwards? You never know if you may find a leak, or a line disconnected further back Nothing is impossible; you could even find a clog in a line? Maybe a line got pinched somewhere...
    Yeah, I'll do just that eventually. Summer doesn't get brutally hot around here, so my A/C is perfectly serviceable for now.
    -Mike
    2005 Lotus Elise, chrome orange, naked carbon fiber front clam, baffled oil pan, rear toe link brace
    1987 Lotus Esprit Turbo HCi
    1999 Saturn SL1, running like a champ
    1981 DMC DeLorean, Alpine head unit + Genesis P5 amplifier + subwoofer, Eibach springs + Houston Shocks, EFI via MS2Extra & Renault Z7U intake manifold, self-installed DPI Spec 2 engine package

  6. #6
    Senior Member Kevin's Avatar
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    Bumping this because I'm having the same problem. Did you ever figure out your issue, Mike?

    I went to a shop because my A/C hadn't been working, figured I needed a recharge since I hadn't turned on my A/C in over a year. Turns out my compressor and refrigerant are fine. Then I noticed the vacuum line wasn't plugged into the hot water valve. That seemed to fix things for the most part but I know it should be colder.

    How likely is it for a hot water valve to fail? I don't have a vacuum gauge at the moment to test mine. Is it more likely to be a vacuum leak elsewhere?

  7. #7
    Delorean Guru
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    I would have to check but as I remember it you only have vacuum on that valve in MAX to close it ONLY when in that position. All other times there is no vacuum on that valve and it is open. The valve does fail. They either leak or get hard to move, too hard for the vacuum to move it. Usually the hoses and clamps also need to be changed. Besides the hose getting kinked, crushed, cut, or a hole worn into it you can also have a problem with the Mode switch especially if it is hissing and is hard to turn. You rebuild it with a new rubber part. Even if the valve is open you should still have noticeable cooling. If you are not getting enough cooling some of the causes include:
    Using R-134
    Dirty evap coil and/or condenser coil
    Cooling fans not running
    Over or under charge of refrigerant
    A/C belt slipping
    Fan running backwards
    Vents leaking into the doors, boot not on right on the center vents and leaking into the dash making the radio nice and cold
    Make sure the Temp is all the way to blue and the cable is hooked up.
    David Teitelbaum






    QUOTE=Kevin;62790]Bumping this because I'm having the same problem. Did you ever figure out your issue, Mike?

    I went to a shop because my A/C hadn't been working, figured I needed a recharge since I hadn't turned on my A/C in over a year. Turns out my compressor and refrigerant are fine. Then I noticed the vacuum line wasn't plugged into the hot water valve. That seemed to fix things for the most part but I know it should be colder.

    How likely is it for a hot water valve to fail? I don't have a vacuum gauge at the moment to test mine. Is it more likely to be a vacuum leak elsewhere?[/QUOTE]

  8. #8
    Senior Member Kevin's Avatar
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    Quote Originally Posted by David T View Post
    I would have to check but as I remember it you only have vacuum on that valve in MAX to close it ONLY when in that position. All other times there is no vacuum on that valve and it is open. The valve does fail. They either leak or get hard to move, too hard for the vacuum to move it. Usually the hoses and clamps also need to be changed. Besides the hose getting kinked, crushed, cut, or a hole worn into it you can also have a problem with the Mode switch especially if it is hissing and is hard to turn. You rebuild it with a new rubber part. Even if the valve is open you should still have noticeable cooling. If you are not getting enough cooling some of the causes include:
    Using R-134
    Dirty evap coil and/or condenser coil
    Cooling fans not running
    Over or under charge of refrigerant
    A/C belt slipping
    Fan running backwards
    Vents leaking into the doors, boot not on right on the center vents and leaking into the dash making the radio nice and cold
    Make sure the Temp is all the way to blue and the cable is hooked up.
    David Teitelbaum
    Thanks a lot, David. Yes I've been leaving it on MAX with temp all the way to blue with fan speed set to 4. The cooling is noticeable but it's just not enough (perhaps I could use the thermometer on my multimeter to get an actual temp reading if that's helpful, don't have one of those laser gauges). I've also plugged my door vents to send all the cool air out of the center vents.

    My system is R-134a, I can hear the cooling fans running when the compressor cycles, pretty sure my refrigerant levels are good as I just had it checked this week, though can't say anything about the A/C belt slipping. I'll have to look into the evap/condenser coils too.

    The valve may be the original, and I do have a relatively high-mileage car (~92k), so it could be that it's getting worn out. I'll also listen for excessive hissing around the mode switch. I also MAY have kinked that plastic tube that goes into the valve, I'll see if I can tape that up. So for now, I think my main concentration is on the vacuum side of things.

  9. #9
    EFI Guy
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    I never got around to figuring the problem out. I'm getting ~45 degrees out of the vents, which is plenty fine by me.
    -Mike
    2005 Lotus Elise, chrome orange, naked carbon fiber front clam, baffled oil pan, rear toe link brace
    1987 Lotus Esprit Turbo HCi
    1999 Saturn SL1, running like a champ
    1981 DMC DeLorean, Alpine head unit + Genesis P5 amplifier + subwoofer, Eibach springs + Houston Shocks, EFI via MS2Extra & Renault Z7U intake manifold, self-installed DPI Spec 2 engine package

  10. #10
    Delorean Guru
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    Using -134 will decrease your capacity about 10% and that's if the conversion was done properly. Blocking vents will reduce the airflow over the evap coil and reduce your capacity. All of the vents need to be open. You can manually block the heater valve closed with a zip tie and not worry about the vacuum for now but I doubt it will make much difference. Check that the recirc door is closed. No need to bring in the hot, outside air. I forgot if it is open in MAX but if it is then you are better off closing it by going to NORM.
    David Teitelbaum




    Quote Originally Posted by Kevin View Post
    Thanks a lot, David. Yes I've been leaving it on MAX with temp all the way to blue with fan speed set to 4. The cooling is noticeable but it's just not enough (perhaps I could use the thermometer on my multimeter to get an actual temp reading if that's helpful, don't have one of those laser gauges). I've also plugged my door vents to send all the cool air out of the center vents.

    My system is R-134a, I can hear the cooling fans running when the compressor cycles, pretty sure my refrigerant levels are good as I just had it checked this week, though can't say anything about the A/C belt slipping. I'll have to look into the evap/condenser coils too.

    The valve may be the original, and I do have a relatively high-mileage car (~92k), so it could be that it's getting worn out. I'll also listen for excessive hissing around the mode switch. I also MAY have kinked that plastic tube that goes into the valve, I'll see if I can tape that up. So for now, I think my main concentration is on the vacuum side of things.
    Last edited by Ron; 06-29-2012 at 03:24 PM.

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