HVAC controls hiss when off

byarnell05

byarnell05

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Aug 21, 2020
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Washington
Is it normal for the AC/Heater control to hiss when you turn it to the off position? I pulled out the control panel and can feel air coming out of the control valve (not exactly sure thats the name, the dial on the far right). I checked all the vacuum lines and they look ok, it seems like its coming out of the control itself. This can't be normal? I'm about to pull the trigger on ordering a new one but thought I should ask here first.
 
Hiss for a second or continuously? Mine hiss and groan a little while the doors are actuating between selections, but if it's full time, you have a vacuum leak. Probably a line and not the control unit itself.
 
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SkylinesSuck said:
Hiss for a second or continuously? Mine hiss and groan a little while the doors are actuating between selections, but if it's full time, you have a vacuum leak. Probably a line and not the control unit itself.
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Ya it hisses for quite a while. Goes away if I switch it to any other setting. Theres a bit of play in the control unit and if I push it together the air I can feel goes away, thats why I suspected the control unit.
 
When you turn it to off I think it closes a door on the intake side of the whole HVAC box. If that line is broken or damaged or the actuator is is leaking it'll just bleed vacuum the entire time it's in the off position. You shouldn't "feel" any air, all those lines suck, they don't blow and in my experience it's not easy to feel a vacuum leak but you might be better at it.
 
Interesting. You might be right then. Pop it out with everything still connected and see what's what. It's easy to get at.
 
byarnell05 said:
Just in case anyone comes across this later on. I ordered a new control module (5013833AA) and the short vacuum hose section (5013831AA) and the hiss went away completely.
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Sorry to reboot an old thread, but I'm having g the same issue with mine. Was working fine the other day now it just hisses when the system is off AND, I can no longer direct the air to anything besides defrost and floor. So was wondering, when yours was having the hissing issue were you able to direct airflow or not? Trying to figure out if I just need to order a new control panel
 
Navygz19 said:
Sorry to reboot an old thread, but I'm having g the same issue with mine. Was working fine the other day now it just hisses when the system is off AND, I can no longer direct the air to anything besides defrost and floor. So was wondering, when yours was having the hissing issue were you able to direct airflow or not? Trying to figure out if I just need to order a new control panel
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I would appear that above post is the last one this user made, and he was last 'seen' in June of 2022.
 
Navygz19 said:
Sorry to reboot an old thread, but I'm having g the same issue with mine. Was working fine the other day now it just hisses when the system is off AND, I can no longer direct the air to anything besides defrost and floor. So was wondering, when yours was having the hissing issue were you able to direct airflow or not? Trying to figure out if I just need to order a new control panel
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Generally, broken vacuum lines are more common than defective controls.
 
Chris said:
^ this
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Yes. Thank you. I'm fully aware of that, it was just a question about the symptoms RE: the ability to change the air flow. OP stated they ordered a new CM in addition to short vacuum hose which I also plan on doing.
 
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