How do I tell if this is good and working? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Murphy IRE · 05-01-2010, 12:42 PM

OK it's a Control Head Vacuum Switch. It's on the control panel for heat and defrost.
Before I put the control panel back in, I want to make sure this switch does what it is supposed to do. I checked and it doesn't hold a vacuum. Is it supposed too? The switch moves when the lever is thrown. I have a diagram and the hoses are in the correct place.
Any suggestions?

raverider · 05-01-2010, 05:31 PM

it should not hold a vacuum because there will be a continuous vacuum from the engine holding it in the position selected, otherwise the vacuum line would collapse? just a guess

Indyuke · 05-01-2010, 06:40 PM

Raverider is right. It's just a vacuum switch, porting vacuum one way or another.

Murphy IRE · 05-02-2010, 08:28 AM

How would it change the direction of the vacuum, if the vacuum isn't being held? I know my actuator is shot ( it will pull down,but it won't stay down) and because of that, the heater valve stays open causing the heat to always flow into the core.
I think this is the last problem on my heat system, I just need to figure out where to get a new one or is there a way to repair the old one.
Thanks,

into69z · 05-02-2010, 10:05 AM

i had a problem with mine-it didn't pull vacuum to keep the heater valve closed. I found the end of the vacuum line just hanging down and upon furhter investigation, found the orface port it was attached to was full of road dust. I took a very small drill bit and by hand was able to clean out that three position diverter, then I ran vacuum line while the unit was hanging down to check the system for function. One mistake I made was using too large vacuum hose-I now have the correct diameter hose and all is working fine.

into69z · 05-02-2010, 10:08 AM

...........also-I think the vacuum is held in the vacuum canister on the a/c heater box in the engine compartment-this valve is just a directional switch, hope it helps....

Murphy IRE · 05-03-2010, 10:55 PM

After a lot of research. GM has had problems with this design, but it was great for sales; because everyone replaced all the other valves before finding the real problem! There is a cheap diaphram gasket on the inside. It holds vacuum and allows the vacuum to directed from one system to the other. Apparently, in 1992 on the inline 4cl Chevy Cavalier they were still using this part. Same on 84 Olds. I'm sure they aren't an exact fit. I found a sight in CA that specializes in corvette parts and the top half, it appears to be identical; but the bottom linkage is different (A possibility for a mix and match}. I will try the dealer on the Olds and Cavalier info in the morning. The name was changed to "Rotary Switch" for the vacuum control valve on the heater switch. If they don't work. The Germans on 64-72 Benz's have an electronic assited vacuum valve. Turn it off or on to direct the vacuum. You can buy new from a place in AZ or go to the local Benz JY and pull for a lot less. Apparently they have a longer life. I'll update with the final solution.

05-01-2010, 12:42 PM	#1
Murphy IRE Registered User Join Date: Oct 2009 Location: South Denver Metro, CO Posts: 385	How do I tell if this is good and working? OK it's a Control Head Vacuum Switch. It's on the control panel for heat and defrost. Before I put the control panel back in, I want to make sure this switch does what it is supposed to do. I checked and it doesn't hold a vacuum. Is it supposed too? The switch moves when the lever is thrown. I have a diagram and the hoses are in the correct place. Any suggestions? Attached Images

05-01-2010, 05:31 PM	#2
raverider Registered User Join Date: Apr 2009 Location: duluth minnesota Posts: 30	Re: How do I tell if this is good and working? it should not hold a vacuum because there will be a continuous vacuum from the engine holding it in the position selected, otherwise the vacuum line would collapse? just a guess

05-01-2010, 06:40 PM	#3
Indyuke Registered User Join Date: Feb 2008 Location: Lake Stevens, WA Posts: 623	Re: How do I tell if this is good and working? Raverider is right. It's just a vacuum switch, porting vacuum one way or another.

05-02-2010, 08:28 AM	#4
Murphy IRE Registered User Join Date: Oct 2009 Location: South Denver Metro, CO Posts: 385	Re: How do I tell if this is good and working? How would it change the direction of the vacuum, if the vacuum isn't being held? I know my actuator is shot ( it will pull down,but it won't stay down) and because of that, the heater valve stays open causing the heat to always flow into the core. I think this is the last problem on my heat system, I just need to figure out where to get a new one or is there a way to repair the old one. Thanks,

05-02-2010, 10:05 AM	#5
into69z "brand new second-hand" Join Date: Feb 2007 Location: White House, Tennessee Posts: 526	Re: How do I tell if this is good and working? i had a problem with mine-it didn't pull vacuum to keep the heater valve closed. I found the end of the vacuum line just hanging down and upon furhter investigation, found the orface port it was attached to was full of road dust. I took a very small drill bit and by hand was able to clean out that three position diverter, then I ran vacuum line while the unit was hanging down to check the system for function. One mistake I made was using too large vacuum hose-I now have the correct diameter hose and all is working fine. __________________ Steve 69 3/4t custom camper tilt,am/fm,speed warning,air gauge,buddy buckets,aux battery, big block,p/s,p/b,a/c 67 Camaro 96 Impala ss-sold 04 hybrid Honda-saving gas for the blue truck!:b69:

05-02-2010, 10:08 AM	#6
into69z "brand new second-hand" Join Date: Feb 2007 Location: White House, Tennessee Posts: 526	Re: How do I tell if this is good and working? ...........also-I think the vacuum is held in the vacuum canister on the a/c heater box in the engine compartment-this valve is just a directional switch, hope it helps.... __________________ Steve 69 3/4t custom camper tilt,am/fm,speed warning,air gauge,buddy buckets,aux battery, big block,p/s,p/b,a/c 67 Camaro 96 Impala ss-sold 04 hybrid Honda-saving gas for the blue truck!:b69:

05-03-2010, 10:55 PM	#7
Murphy IRE Registered User Join Date: Oct 2009 Location: South Denver Metro, CO Posts: 385	Re: How do I tell if this is good and working? After a lot of research. GM has had problems with this design, but it was great for sales; because everyone replaced all the other valves before finding the real problem! There is a cheap diaphram gasket on the inside. It holds vacuum and allows the vacuum to directed from one system to the other. Apparently, in 1992 on the inline 4cl Chevy Cavalier they were still using this part. Same on 84 Olds. I'm sure they aren't an exact fit. I found a sight in CA that specializes in corvette parts and the top half, it appears to be identical; but the bottom linkage is different (A possibility for a mix and match}. I will try the dealer on the Olds and Cavalier info in the morning. The name was changed to "Rotary Switch" for the vacuum control valve on the heater switch. If they don't work. The Germans on 64-72 Benz's have an electronic assited vacuum valve. Turn it off or on to direct the vacuum. You can buy new from a place in AZ or go to the local Benz JY and pull for a lot less. Apparently they have a longer life. I'll update with the final solution.

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