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#1 |
Registered User
![]() Join Date: May 2015
Location: Ashland, Ohio
Posts: 579
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A/c climate control
Does anyone know why some unit have 2 vacuum nozzles and some have 3?
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#2 |
Registered User
![]() Join Date: Aug 2013
Location: Atlanta, GA
Posts: 702
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Re: A/c climate control
They do the same thing just changed throughout the years. The difference is how the vacuum hoses are routed. In particular one supplies vacuum to a hot water valve which should be open with vacuum applied. The other does exactly the opposite. As long as you have the right controller, hot water shut off and vacuum routing you can use either. There is a recent post that shows the differences in hose routing.
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1968 C10 292/3 spd - sold 1969 K10 350/3 spd/205 - sold 1971 K5 350/4 spd/ 205 - sold 1970 K20 350/350/205 - sold 1969 K20 396/400/205 - work in process |
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#3 |
Registered User
Join Date: Mar 2015
Location: Utah
Posts: 750
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Re: A/c climate control
do you have a link to said post?
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#4 |
member #16
![]() Join Date: Dec 1999
Location: Yuba City Ca.
Posts: 3,618
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Re: A/c climate control
Here is a thread that shows both hose routes.
http://67-72chevytrucks.com/vboard/s...ad.php?t=76770
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#5 |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: A/c climate control
Yes, I am a master of this topic by necessity, ran into issues on my truck. See the other thread for routing.
Long story short, however, they went from a "vacuum switched on" to "vacuum switched off" heater control valve and so needed a third port on the switch that is backwards from the cowl vent. In later years they got both vacuum solenoid and heater control switch on the same circuit, operating in the same direction, so they only needed the one signal. So it becomes a basic vacuum switch in that case, one in and one out.
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#6 |
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Location: Atlanta, GA
Posts: 702
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![]() ![]() http://67-72chevytrucks.com/vboard/s...d.php?t=518197
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1968 C10 292/3 spd - sold 1969 K10 350/3 spd/205 - sold 1971 K5 350/4 spd/ 205 - sold 1970 K20 350/350/205 - sold 1969 K20 396/400/205 - work in process |
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#7 |
Registered User
![]() Join Date: May 2015
Location: Ashland, Ohio
Posts: 579
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Re: A/c climate control
Thanks for all the great info. I really appreciate it.
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#8 |
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Join Date: Feb 2012
Location: Ruskin Florida
Posts: 4,560
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Re: A/c climate control
Does this mean that the heater valve was different too?
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#9 |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: A/c climate control
Yes, a 2-port uses a different valve than a 3-port. It works backwards (on vs off under vacuum).
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1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#10 |
Registered User
![]() Join Date: Jan 2012
Location: Spruce Grove, Alberta
Posts: 237
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Re: A/c climate control
I realize this is an older post but I was having issues with my 3 port control head vacuum switch so I had to get my vacuum tester hooked up and get this figured out.
My 3 port vacuum switch has part number 7292032-1 cast into the pot metal. These have numbers 1, 2 and 3 cast next to the three ports. Mounted correctly to the air conditioning/ heater sliding control lever assembly under the dash port 1 would be closest to the passenger side, port 2 in the middle and port 3 closest to the driver side. Port 1 is vacuum in from your vacuum canister under the hood. This has to be vacuum in for this 3 port valve to work correctly. Port 1 is common with port 2 when the uppermost lever is moved to INSIDE air. In this position vacuum from the vacuum canister draws a vacuum in port 2 and the vacuum line attached to the outside air door diaphragm closing this flap. Vacuum from another line tee'd to the vacuum line attached to port 2 acts on the vacuum canister attached to and opens the recirculating air door on the passenger side kick panel. At the same time the correct water valve is closed from a lack of vacuum in port 3 line. Port 1 is common with port 3 when the uppermost lever is moved to OUTSIDE air and then remains common as the lever is moved all the way to the right DE-ICE label. In this position port 3 line vacuum draws the water valve open allowing circulation of coolant. Lack of vacuum in port 2 allows the spring to close the inside kick panel vent and the spring to open the outside air door diaphragm. My 3 port control head switch could not be taken apart. it appears to be held together with a rivet through the center of the assembly. The spring clip under the large head of the rivet is keeping tension on the two halves sealing the vacuum control head switch as good as possible with 1972 technology. Hope this helps someone. |
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Tags |
air conditioning, heater, vacuum |
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