HVAC VACUUM CONTROLS

Technical Question and Answer - On topic to 71-74 Plymouth B-bodies only.

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Hugh
Satellite Sebring (RH)
Posts: 54
Joined: Tue Dec 22, 2009 9:37 am
My Cars: 1973 Plymouth Satellite Sebring 318/904/8.25
1978 Dodge D150 400/727/9.25
Location: Dannemora, NY

HVAC VACUUM CONTROLS

Post by Hugh » Sun Sep 03, 2017 10:27 am

I am working on my 1973 Satellite, factory air car. I'm trying to get HVAC system to switch between modes, i.e., defrost, heat, vent, a/c, etc. I replaced heater core, necessitating heater box removal. I checked all doors for operation with hand vac pump, all worked perfectly. After reinstalling heater box, I ran new vacuum lines from intake manifold to vacuum reservoir, then from reservoir into car. Checked for vacuum at molded head that plugs into control, and have 17 pounds of vacuum. I can plug hand pump into molded head that plugs into control and easily manipulate hvac doors through molded control head plug in with just a pump or two with hand vac pump. This all lead me to believe control head was faulty. Against my better judgement, I. Bought a used control off eBay, and that one kind of gives me every mode at once, control door wise, as in defrost, heat, vent all at once. I kind of think I got a faulty control unit. After all, it was same age mine was within a year or two either way. I think I should have gone NOS route. I see they are re popping the six button push button controls like used in e bodies. Must be a demand for them! Any thoughts, anyone? :help:

Hugh
Satellite Sebring (RH)
Posts: 54
Joined: Tue Dec 22, 2009 9:37 am
My Cars: 1973 Plymouth Satellite Sebring 318/904/8.25
1978 Dodge D150 400/727/9.25
Location: Dannemora, NY

Re: HVAC VACUUM CONTROLS

Post by Hugh » Wed Sep 06, 2017 7:23 pm

Ok, I broke down yesterday and ordered an NOS replacement . Gotta go by part number on these, as they are commonly listed as 1972-80 Dodge truck. I'll let you know how this turns out, but I think this is going to be it! BTW, the HVAC vacuum control is correct for those years of Dodge truck as well, and are commonly listed wrong as a 6 push button control, which is being repopped, but not the one we all need.

Hugh
Satellite Sebring (RH)
Posts: 54
Joined: Tue Dec 22, 2009 9:37 am
My Cars: 1973 Plymouth Satellite Sebring 318/904/8.25
1978 Dodge D150 400/727/9.25
Location: Dannemora, NY

Re: HVAC VACUUM CONTROLS

Post by Hugh » Sat Sep 09, 2017 7:16 pm

Tried NOS replacement, same issues. Vent only. I have vacuum in and individually at connector between HVAC control and heater box. All doors move individually with vac pump, but not plugged in to HVAC control. I'm beginning to think this system may be vacuum loaded at all times, not just individual lines to what is being actuated.i think I may have a breach somewhere I haven't found yet that is wasting my vacuum. I was able to reach my fresh air door and floor actuator lines and check with vacuum gauge while car was running and not able to get a vacuum reading, yet I could move those doors from the control head that plugged into control unit easily with hand pump! That's why I think system is completely vacuum loaded at all times and that there is a breach somewhere.

moparite
GTX (RS)
Posts: 237
Joined: Tue Apr 21, 2009 8:27 am
My Cars: 1971 Road Runner 4speed FJ6 air grabber car. And yes i have the
build sheet to prove it. NO IT'S NOT FOR SALE!
Location: South Jersey

Re: HVAC VACUUM CONTROLS

Post by moparite » Sun Sep 10, 2017 9:37 am

When you did the heater core are you sure you put the vac lines back the way they came off? The actuators are working with the hand pump so that's not the issue. I would take off the vac lines off(mark them of course) the actuators and check and see if you hear the vac change between the lines when you move the HVAC control. If not the issue is the control. Also you may want to put a vac gauge on the vac line coming in the HVAC control and see if you have adequate vac. If there is a leak it may not be enough to work the actuators.

Hugh
Satellite Sebring (RH)
Posts: 54
Joined: Tue Dec 22, 2009 9:37 am
My Cars: 1973 Plymouth Satellite Sebring 318/904/8.25
1978 Dodge D150 400/727/9.25
Location: Dannemora, NY

Re: HVAC VACUUM CONTROLS

Post by Hugh » Sun Sep 10, 2017 7:41 pm

moparite wrote:When you did the heater core are you sure you put the vac lines back the way they came off? The actuators are working with the hand pump so that's not the issue. I would take off the vac lines off(mark them of course) the actuators and check and see if you hear the vac change between the lines when you move the HVAC control. If not the issue is the control. Also you may want to put a vac gauge on the vac line coming in the HVAC control and see if you have adequate vac. If there is a leak it may not be enough to work the actuators.
Hi, thanks for the reply! I have 17 inches of vacuum coming into control unit. I just found a very good section in my FSM on the operation of HVAC system. I guess I'll go off from that and start checking for vacuum on lines according to the FSM. I thought about what you said earlier about not putting vac lines back correctly when I took heater box apart, and I think I did them one a a time for just that reason. I've had the car 10 plus years and this has been an issue from the beginning. I want to fix it so I can pull the dash and put new dash harness in and get rid of dash cap and put in new dash pad. Just want to wrap up the whole dash area! Then I put in classic auto air compressor and get a/c working again! Already put in new engine harness!

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