part numbers for heat/AC vacuum switch?

[PM27G0D]

I bought an NOS vacuum switch on eBay, part #3431020...for my '70 Suburban non-ATC wagon. The vacuum part now works great, but the AC compressor and blower motor stay on all the time regardless of what mode button is depressed. I've heard that Chrysler did that on purpose in some later years, but my original switch didn't do that and I don't want that. The part number stamped on the NOS switch is the same number as the original one I replaced though..so I'm not sure whether the new switch is defective or what....Has anyone had this switch fail in this mode?
I know there are a variety of part numbers that these switches supposedly interchange with, but I never see any mention of which ones keep the blower and compressor energized and which ones don't. I could put an external switch in for the compressor, but I really want to keep everything "stock".
Anyone been down this road?

 

[3175375]

I bought an NOS vacuum switch on eBay, part #3431020...for my '70 Suburban non-ATC wagon. The vacuum part now works great, but the AC compressor and blower motor stay on all the time regardless of what mode button is depressed. I've heard that Chrysler did that on purpose in some later years, but my original switch didn't do that and I don't want that. The part number stamped on the NOS switch is the same number as the original one I replaced though..so I'm not sure whether the new switch is defective or what....Has anyone had this switch fail in this mode?
I know there are a variety of part numbers that these switches supposedly interchange with, but I never see any mention of which ones keep the blower and compressor energized and which ones don't. I could put an external switch in for the compressor, but I really want to keep everything "stock".
Anyone been down this road?

Check the switch and refer to the FSM.

If I remember correctly, the compressor is controlled via the temperature set lever, once the mode via the switch you installed is set to max AC, defrost or air conditioning mode.

There’s a bit to review to understand the system.

I went through this in my 69 Fury III vert, here:

Double Doofus - Air conditioning on a 69 Fury III vert

 

[PM27G0D]

Check the switch and refer to the FSM.

If I remember correctly, the compressor is controlled via the temperature set lever, once the mode via the switch you installed is set to max AC, defrost or air conditioning mode.

There’s a bit to review to understand the system.

I went through this in my 69 Fury III vert, here:

Double Doofus - Air conditioning on a 69 Fury III vert

Was your compressor energized even in the "OFF" switch mode? Mine is with this NOS switch assembly...same part number stamped on it as yours.

 

[3175375]

Was your compressor energized even in the "OFF" switch mode? Mine is with this NOS switch assembly...same part number stamped on it as yours.

No
It isn’t energized until a mode is selected. There is a temp switch that prevents or engages the compressor (I don’t recall which), depending upon the outside air temperature.

 

[PM27G0D]

No
It isn’t energized until a mode is selected. There is a temp switch that prevents or engages the compressor (I don’t recall which), depending upon the outside air temperature.

Wouldn't that be if the system was the Automatic Temp Control AC option? Mine is the basic manual temp control version. Maybe this NOS switch is just defective.

 

[3175375]

Wouldn't that be if the system was the Automatic Temp Control AC option? Mine is the basic manual temp control version. Maybe this NOS switch is just defective.

The temperature switch is to eliminate fogging up the windshield.
It’s described in the documentation that I referenced in my post.

 

[Stoffauge]

I bought an NOS vacuum switch on eBay, part #3431020...for my '70 Suburban non-ATC wagon. The vacuum part now works great, but the AC compressor and blower motor stay on all the time regardless of what mode button is depressed. I've heard that Chrysler did that on purpose in some later years, but my original switch didn't do that and I don't want that. The part number stamped on the NOS switch is the same number as the original one I replaced though..so I'm not sure whether the new switch is defective or what....Has anyone had this switch fail in this mode?
I know there are a variety of part numbers that these switches supposedly interchange with, but I never see any mention of which ones keep the blower and compressor energized and which ones don't. I could put an external switch in for the compressor, but I really want to keep everything "stock".
Anyone been down this road?

Morning bud,

I thought I am the only one with that problem or did something wrong!!! I ordered the same switch NOS and def got the right replacement for mine - I checked parts book and it´s 100% the right switch I bought. Since its installed the different doors (window, front, etc) are still not working although I got vakuum at the switch BUT:

my blower is on all the time and it made me already pull the fuse. Actually thought already I bought a broken NOS one and wasted 100$........ really hope we can fix it together!!

71 Sport Fury A/C without ATC.

 

[3175375]

Here’s another thread that might help you both:

Rebuilding the ac/heater control switch

It’s important to understand the entire climate control system.

 

[Stoffauge]

I went through this thread before I bought the NOS switch. Thats why I came to the point I would need a new switch. But it doesnt answer my question if the NOS switch I got is maybe broken already because of beeing old and brittle...... I really hope not so. Next time I would buy a repopped one I guess. Gonna go through it anyways, thanks for the link 3175375

 

[3175375]

I went through this thread before I bought the NOS switch. Thats why I came to the point I would need a new switch. But it doesnt answer my question if the NOS switch I got is maybe broken already because of beeing old and brittle...... I really hope not so. Next time I would buy a repopped one I guess. Gonna go through it anyways, thanks for the link 3175375

Maybe the switch is bad. You should be able to ohm it out to verify incorrect operation.

 

[Stoffauge]

Maybe the switch is bad. You should be able to ohm it out to verify incorrect operation.

Oh please no! SO why is NOS that expensive? In that case this old switch is as bad mine before just because of age. So why charging so much for this NOS part? You know the results I need to get to verify it´s correct or not?

 

[PM27G0D]

Oh please no! SO why is NOS that expensive? In that case this old switch is as bad mine before just because of age. So why charging so much for this NOS part? You know the results I need to get to verify it´s correct or not?

What part number was on your NOS switch?

 

[Stoffauge]

Plymouth 1968-1974 NOS OEM MoPAR A/C Heater Vacuum Switch 3502126 5 Button Type | eBay

NOS OEM Five Button MoPar A/C Heater Vacuum Push Button Switch OEM Number 3502126. This is a new switch with 7 vacuum hose nipples and 5 electrical terminals. This replaces many different MoPar switches (3431020, 2820487, 3895033, 3895790).​

 

[3175375]

Oh please no! SO why is NOS that expensive? In that case this old switch is as bad mine before just because of age. So why charging so much for this NOS part? You know the results I need to get to verify it´s correct or not?

Check the switch operation. Maybe something else is going on. I thought I could simply charge the system on my car, but the person who installed the compressor connected it backwards (high and low pressure sides).

My point is, you have stated a symptom, and haven’t found the root cause yet.

Don’t be so worried about the switch you bought, until you have the actual problem identified.


By the way, I bought the mode control switch from Jegs.

 

[PM27G0D]

My original was 3431020 and the NOS one I bought was the very same number. Is your compressor and blower energized all the time with your new switch? I can understand it being on for the DEF mode, but not in "OFF". My original switch shut off the compressor and blower in the "OFF" mode.

 

[Stoffauge]

My original was 3431020 and the NOS one I bought was the very same number. Is your compressor and blower energized all the time with your new switch? I can understand it being on for the DEF mode, but not in "OFF". My original switch shut off the compressor and blower in the "OFF" mode.

Same with me. Blower always on but compressor not working because unattached (installed but not plugged in - out of order) . The "broken switch" did shut off the blower like it should. SInce I got the NOS one blower always running. Pulled fuse already

 

[PM27G0D]

Same with me. Blower always on but compressor not working because unattached (installed but not plugged in - out of order) . The "broken switch" did shut off the blower like it should. SInce I got the NOS one blower always running. Pulled fuse already

Sounds like we have the very same issue with the NOS switches. I emailed OER that makes the repro switch and asked them in what modes the blower and compressor are energized. I haven't heard back yet, but will post here when I do.

 

[Stoffauge]

Sounds like we have the very same issue with the NOS switches. I emailed OER that makes the repro switch and asked them in what modes the blower and compressor are energized. I haven't heard back yet, but will post here when I do.

We do 100%. The only thing I kinda think the NOS switch is working is the fact that the blower motor runs all the time. atleast there´s a difference to the "old" one before

 

[PM27G0D]

We do 100%. The only thing I kinda think the NOS switch is working is the fact that the blower motor runs all the time. atleast there´s a difference to the "old" one before

The only good thing about the NOS switch is that the vacuum actuators now have full travel....before they were only moving maybe a quarter of an inch or so.

 

[Stoffauge]

The only good thing about the NOS switch is that the vacuum actuators now have full travel....before they were only moving maybe a quarter of an inch or so.

My vacuum actuators still don´t move an inch. I already checked engine vacuum (16HG) and checked my vacuum reservoir (works fine! ) but yet nothing changes when pushing the buttons...