vacuum trouble?

[PM27G0D]

I've got a '70 Plymouth Suburban that has a very long-term dormant factory AC system. First thing was replacing the inoperative blower motor and this week, took it to a shop that can deal with old car AC systems to evaluate what all is bad and make a decision on a repair or install a retrofit kit with new compressor, etc.
Well, it turned out that all the original components are working and passed the leak test just fine. They were somewhat shocked as was I. They changed the oil in it and charged it with R134 and...where it blows....it's quite cold.
Problem is on the interior side. I can hear the vacuum changing a little when pushing the buttons from heat to max ac and defrost, but I get very little air out of the dash vents or defrost and never get any air out of the lower vent above the tunnel where the heat would normally come out towards the driver's feet area. Most of the air is coming out of about a 3 inch round plastic fitting on the passenger side. It looks like there might have been some sort of flexible duct that is supposed to go there. I've been readking online that the vacuum/control switches become problematic after all these years and I'm wondering if the various vacuum actuators are just not getting enough vacuum and not opening or closing fully.
If there is supposed to be some flexible duct connected to where all the air is blowing out, where does the other end of it connect and could that be the whole problem?
Thanks for any insights on this. I'm still in shock over the system actually sort of working after so many years!

 

[CBODY67]

I suspect there should be an illustration of the hvac duct system in the appropriate Chrysler Corp Factory Service Manual. www.mymopar.com Plus a chart of which actuator is active in what button position, IIRC.

Do track the vac supply line from the intake manifold to inside. I suspect that once it gets inside, with nobody messing with them over the years, the apparently higher-silicone vac lines can still be in good shape. Just my gut suspicion. It is also possible that the white grease on the linkages on the hvac case has dried or gotten stiff, so some modern spray lube might be needed for ease of actuation.

Usually, the default mode for lack of vacuum to the system is the defroster and heater locations, at the same time.

While you're down there, checking the heater duct output, put a piece of duct take over the top 1/2 of the driver's side of that duct. This will make the output on EACH side the same, rather than being biased toward the lh side. That little piece of tape will greatly decrease any complants of "My feet are cold" by the rh frt seat passenger, by observation.

Do keep an eye on the condenser. On our '72 Newport, we got one from the salvage yard. I took it to a radiator shop we used and got it pressure checked, which it passed. Put it on, charged the system, and all was well . . . until it started leaking within a week. Aged solder on the connections, with an oil trail from them. So much for that deal! This was when the car was about 10 years old.

Glad you've had good luck getting things going again!
CBODY67

 

[PM27G0D]

I suspect there should be an illustration of the hvac duct system in the appropriate Chrysler Corp Factory Service Manual. www.mymopar.com Plus a chart of which actuator is active in what button position, IIRC.

Do track the vac supply line from the intake manifold to inside. I suspect that once it gets inside, with nobody messing with them over the years, the apparently higher-silicone vac lines can still be in good shape. Just my gut suspicion. It is also possible that the white grease on the linkages on the hvac case has dried or gotten stiff, so some modern spray lube might be needed for ease of actuation.

Usually, the default mode for lack of vacuum to the system is the defroster and heater locations, at the same time.

While you're down there, checking the heater duct output, put a piece of duct take over the top 1/2 of the driver's side of that duct. This will make the output on EACH side the same, rather than being biased toward the lh side. That little piece of tape will greatly decrease any complants of "My feet are cold" by the rh frt seat passenger, by observation.

Do keep an eye on the condenser. On our '72 Newport, we got one from the salvage yard. I took it to a radiator shop we used and got it pressure checked, which it passed. Put it on, charged the system, and all was well . . . until it started leaking within a week. Aged solder on the connections, with an oil trail from them. So much for that deal! This was when the car was about 10 years old.

Glad you've had good luck getting things going again!
CBODY67

Are any of those linkages that may need lubrication accessible without taking the whole under dash unit apart? I'll take a look at the vacuum source to the interior when I'm at the car later today. I did order a new ac/heat vacuum switch as I've read those are often trouble.

 

[CBODY67]

I'm not sure they are as troublesome as some might indicate. They used them for ages. Even some motorhome people use mid-'70s Chrysler vac swithes.

Tha main linkages I was mentioning are see-able from the floorboard. No disassembly.

Keep us posted,
CBODY67

 

[PM27G0D]

I'm not sure they are as troublesome as some might indicate. They used them for ages. Even some motorhome people use mid-'70s Chrysler vac swithes.

Tha main linkages I was mentioning are see-able from the floorboard. No disassembly.

Keep us posted,
CBODY67

Update on the issue. Checked the operation of the actuators and they were barely moving when changing modes. We replaced the control switch with an NOS one and now, the actuators fully engage....but the new switch has a problem that the contacts that energize the compressor clutch are not working properly. The compressor is staying engaged all the time so we have to unplug the clutch at the compressor to shut it off. I guess I'll have to get another one of these switches. We also found two big pieces of plastic ductwork in the dash are missing. The big one from the airbox to the center dash vents, and the plastic duct that connects the passenger side dash vent to the airbox. I"m going to look up the part numbers for those two pieces in case some one has them, or...worst case, a trip to the junkyard.

 

[CBODY67]

Check the model year application for the NOS switch you purchased. Reason I mention that is that for '72 and possibly '73 C-body cars, the a/c compressor was supposed to run continuously, even when the "OFF" button was pushed. Also, the fan speed was super slow when "OFF".

When we bought our new '72 Newport, I noticed that the a/c compressor ran all of the time. Could not turn it off! I asked the old-line Chrysler service manager at the local dealership (where the car was bought) about this and he said "That's normal" now. I thought that was wrong, but I listened to his comments.

Then, several months later, I read the explanation somewhere. Their "grand orientation" was that in come conditions, when the defroster is first turned on, a cloud of vapor comes out of the ducts, fogging the inside of the windshield . . . sometimes with sub-optimal results. So, it was decided to keep the compressor running all of the time to dehumidify the air in the hvac case. Keeping the fan running at a very low speed to help this along. When I read about the fan speed, I checked our car and it was true.

The issue I had with the a/c compressor being engaged all the time was the power drain it put on the 400 2bbl motor, which was already carrying around more weight with a lower compression ratio than the '66 Newport 383 2bbl was. Which tended to dull of-idle throttle response a bit. THAT was my main concern.

Later, I learned that there was an a/c compressor switch on the heater control cable. About 1/2 way toward "HOT", I could feel and hear a click when the switch was turned off. So I re-indexed the cable end on the water valve and that took care of the compressor running and, as the water valve was closed, no hot water in the heater core. But your car should have a vac-operated water valve, so the "cable hack" will not work.

Only thing you might do is like the law enforcement people did, toggle-switch tha a/c compressor clutch.

CBODY67

 

[PM27G0D]

Check the model year application for the NOS switch you purchased. Reason I mention that is that for '72 and possibly '73 C-body cars, the a/c compressor was supposed to run continuously, even when the "OFF" button was pushed. Also, the fan speed was super slow when "OFF".

When we bought our new '72 Newport, I noticed that the a/c compressor ran all of the time. Could not turn it off! I asked the old-line Chrysler service manager at the local dealership (where the car was bought) about this and he said "That's normal" now. I thought that was wrong, but I listened to his comments.

Then, several months later, I read the explanation somewhere. Their "grand orientation" was that in come conditions, when the defroster is first turned on, a cloud of vapor comes out of the ducts, fogging the inside of the windshield . . . sometimes with sub-optimal results. So, it was decided to keep the compressor running all of the time to dehumidify the air in the hvac case. Keeping the fan running at a very low speed to help this along. When I read about the fan speed, I checked our car and it was true.

The issue I had with the a/c compressor being engaged all the time was the power drain it put on the 400 2bbl motor, which was already carrying around more weight with a lower compression ratio than the '66 Newport 383 2bbl was. Which tended to dull of-idle throttle response a bit. THAT was my main concern.

Later, I learned that there was an a/c compressor switch on the heater control cable. About 1/2 way toward "HOT", I could feel and hear a click when the switch was turned off. So I re-indexed the cable end on the water valve and that took care of the compressor running and, as the water valve was closed, no hot water in the heater core. But your car should have a vac-operated water valve, so the "cable hack" will not work.

Only thing you might do is like the law enforcement people did, toggle-switch tha a/c compressor clutch.

CBODY67

Interesting! The part number on the NOS switch box is the same number as in my parts book and on my old switch...and correct for a '70.
3431020. That part of my old switch worked fine, it was just the vacuum part that was weak. I definitely don't want the compressor running all the time on this car, and especially on it's first real voyage tomorrow...the Hot Rod Power Tour. We may just plug and unplug the compressor under the hood when we want to run it next week. I guess I could unplug one of the pressure switch wires on the dryer to disable it too...wouldn't be as hot on the hands as the compressor connection.
I did notice that when the compressor was running, the two belts running it were bouncing quite a bit. I guess that compressor puts a pulsing load on those belts. Belt tension seems right...although it is at the end of the adjustment range. Perhaps this is normal RV2 stuff? Belts look just fine running with the compressor disengaged.
Now, if I can find these two pieces of missing ductwork....

 

[Big_John]

FWIW, rebuilding the switch. How To Rebuild a Vacuum Heater Control Switch

Just thinking out loud here... What @CBODY67 says about the compressor running is very true for around 1972/3, although I can't say it happens with the '70 cars. IIRC, that's not a function of the vacuum switch.

In the '70 though, there is a "time delay relay" that comes into play to run the compressor during heat and defrost. The compressor runs 2-10 minutes after selecting "heat" or "defrost". I wonder if that's what's going on... Since changing the switch, it might be running correctly now.

Perhaps some study of operation in the FSM might tell you what's going on with that. If you don't have a FSM, download one here: Service Manuals – MyMopar

 

[CBODY67]

Yes, using the low pressure switch connector on the drier can work to disable the compressor easily.

"Belt bounce" is completely normal, no matter how tight you adjust the belts. Adjust them normally and that is all that's needed. You might check the stamp codes to see if they came out of the same batch, for general principles. Used to be that those belts were sold in "matched sets" by Chrysler and others, back then. Allegedly if they were not matched, they might not act right, as in knocking each other off? The bounce will diminish with rpm levels, by observation. And after the compressor gets things cool enough inside.

Have a nice, enjoyable, and safe trip on the Tour!

CBODY67

 

[PM27G0D]

Okay, great to know! I guess I'd just not closely watched the belts on an idling RV2 compressor before. I got these from NAPA several years ago and not as a matched set. They have been probably 1500 miles at least with no issues at all. Of course, that was all with a totally dead AC system!
Do you think the new OER vacuum/control switches are any good and do they turn the compressor on and off? I'm debating on whether to go with one of those, or get another NOS one. The eBay seller I got this one from is givng me a refund on it....nice guy.

 

[CBODY67]

Seems like there are many applications which all use the same of similar switches? No experiences with OER in that area.

Might get a lighted pushbutton switch, for the compressor's power wire, and then use the system like many modern systems which allow the compressor to run or not run without regard to the "vent" selection. Same thing the law enforcement people did.

 

[PM27G0D]

Yeah, I could do that, and might temporarily....but....with my decades long involvement with B and E bodies....my natural inclination is to keep them as close to 100% stock as I can!