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Heater Vacuum Switch

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dltowers View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dltowers Quote  Post ReplyReply Direct Link To This Post Topic: Heater Vacuum Switch
    Posted: Mar/04/2022 at 10:02am
"Heater Vacuum Switch"....

Can anyone tell me the correct part name of the small vacuum switch, circle in red in the below photo?....
And also its' exact function?....

Part # 3217380
Group # 13.036

Vehicle:  Wife's '74 Javelin w/AC

Living in the Houston area, we seldom turn on the heater in the Javelin, but a few days back, while letting the car warm up, I turn on the heater to let hot water flow thru the system....
After the engine had reach operating temperature, no hot air was blowing thru either the defrost vent, dash vents, or floor vents.
I tried on each speed level, still no hot air....
Just room temperature air....

Weather Eye is working correctly, and the control cables are moving correctly....

** The A/C System works great....

I first thought a defective thermostat, but it checked out ok....

However, if I go under the hood and disconnect the small black vacuum hose from the Heater Regulator Valve, then the inside heater starts working and putting out hot air as it should....

The Heater Regulator Valve is also in proper working order....

I believe that the small vacuum switch, that is under the dash, and mounted on the back of the Heater Box may be stuck?....
Possibly from not using the heater for a long period of time?....
The switch has never been replaced....

The first photo below, shows the vacuum switch, circled in red, and the second photo is of a NOS Vacuum Switch that I have had for several years....

Anyone have any ideas or experiences with this issue?....






Edited by dltowers - Mar/04/2022 at 10:04am
Original Owner, 1974 Javelin:
360ci,2v,727TC. Motorola Multiplex with 8-Track.
G4 Plum exterior with 421Q Black Uganda Interior. Purchased on July 16, 1974 from Hooker AMC, Sherman, TX for $4500.20
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Mar/04/2022 at 11:33am
Yes it is used on 73 and 74 Javelins, but it is possible your heater vavle on the engine has a bad diaphram, on the actuator. Newer parts like that, are not as good as the older one made back in the day. It can be stuck, but I think the plunger on the side can be lightly pressed or pulled slightly to release the stuck actuator. A safe lubericant could loosen the pin of the actuator, since dirt and rust build up is common.
71 Javelin SST body
390 69 crank, 70 block & heads
NASCAR SB2 rods & pistons
78 Jeep TH400 w/ 2.76 Low
50/50 Ford-AMC Suspension
79 F150 rear & 8.8 axles
Ford Racing 3.25 gears & 9" /w Detroit locker
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dltowers Quote  Post ReplyReply Direct Link To This Post Posted: Mar/05/2022 at 9:58am
James,
Thanks for the reply....

You say that the small Vacuum Switch on the Heater Box, is called an "Actuator?"....

I tried another Heater Control Valve, but no change, so I believe the Valve is not the problem....

When I remove the small rubber hose from the Heater Valve, I can feel a small amount of suction with my finger?....
With the rubber hose removed, the heater starts working correctly, reattached the rubber hose and hot air stops flowing?

The Weather Eye Control is working correctly, all cables operating....

Below are 2 photos of the type Heater Control Valve that I am using, this type is correct for '73-'74 with A/C....
I was hoping to find a solution without having to remove the Dash to access the Vacuum Switch (Actuator)....




Edited by dltowers - Mar/05/2022 at 10:03am
Original Owner, 1974 Javelin:
360ci,2v,727TC. Motorola Multiplex with 8-Track.
G4 Plum exterior with 421Q Black Uganda Interior. Purchased on July 16, 1974 from Hooker AMC, Sherman, TX for $4500.20
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ramblinrev Quote  Post ReplyReply Direct Link To This Post Posted: Mar/05/2022 at 11:11am
IIRC, the "off" position provides vacuum to close the valve...so warm coolant does not flow. The switch must be what cuts the vacuum and allows the coolant to flow.

Any chance your heater core is plugged?
74 Hornet Hatchback X twins (since 1977)
62 American Convertible (still worth the $50 I spent in 1973!) AMCRC #513, AMO #384
70 AMX 360 4-speed (since 1981)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Mar/05/2022 at 11:19am
Dltowers, the actuator switch is to be mounted so that it opens and closes proper, by how close it mounts to the lever cam. Notice the holes in the mounting tab are slotted. The round head that is on a threaded pin is to move in some and release. You may need to adjust it to allow proper actuation to open the diaphragm to the heater vavle on the engine.
71 Javelin SST body
390 69 crank, 70 block & heads
NASCAR SB2 rods & pistons
78 Jeep TH400 w/ 2.76 Low
50/50 Ford-AMC Suspension
79 F150 rear & 8.8 axles
Ford Racing 3.25 gears & 9" /w Detroit locker
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Mar/05/2022 at 11:29am
Ps. I Think the valve is one way... meaning vacuum end will ge diverted incorrectly if the two tubing connections are reversed. You may need to test by using line connected on one nipple and suck on the tube end. If you are able to suck air, the nipple you tested goes to the vacuum tubing to the heater valve. If you cannot suck air the engine vacuum is to be attached to the end tested. Many who replace them fail to take notice and assume the function is simple. They are lucky sometimes and get it right, as it is a 50/50 shot.
71 Javelin SST body
390 69 crank, 70 block & heads
NASCAR SB2 rods & pistons
78 Jeep TH400 w/ 2.76 Low
50/50 Ford-AMC Suspension
79 F150 rear & 8.8 axles
Ford Racing 3.25 gears & 9" /w Detroit locker
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dltowers Quote  Post ReplyReply Direct Link To This Post Posted: Mar/08/2022 at 2:04am
Thanks for the replies, I believe I now understand how the Switch functions.
Original Owner, 1974 Javelin:
360ci,2v,727TC. Motorola Multiplex with 8-Track.
G4 Plum exterior with 421Q Black Uganda Interior. Purchased on July 16, 1974 from Hooker AMC, Sherman, TX for $4500.20
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/08/2022 at 3:07pm
Originally posted by ramblinrev ramblinrev wrote:

Any chance your heater core is plugged?
That was my thought too. It sounds like the heater gets little use, so the coolant may sit in the core for extended periods (years?) of time. However, I would diagnose the vacuum actuator first.
69 Javelin SST BBO 390 T10
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jaybobby339 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/16/2022 at 5:06pm
I'm working on the same problem currently on my Hornet. There is a check valve coming off the vacuum supply hose off of the intake manifold. I would check that as well. It's a 1/4 inch vacuum hose reduced to 1/8 inch by the check valve and goes into the firewall. At least that's how it is on my hornet 6 cyl with AC. I ordered YG360 to replace it and I'm hoping that will work.
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