1950s 1956 A/C question(s) topic

[J. Gomez]

As I'm getting close to refill my 1956 A5 compressor after a very long delay with other projects I'm considering how to safeguard/protect the compressor?

I overhauled the compressor a few years back new carbon seals, bearing, clutch, etc. as well as the dehydrator/receiver, the compressor was fill with the correct oil viscosity 525 for R12. All the lines were cleaned and checked for any leaks at each connections.

One of my concerns is parts for this type of compressor are becoming very hard to find and almost "unobtanium" at this time, the carbon seal is one of them. Looking at the original layout the compressor will continue cycling if the Freon charge is low or totally gone, so no safeguard if this happens. The compressor has the high pressure valve that is fine but again no other safeguard to de-activate the clutch if either low or high pressure is present.

I'm curious if anyone have try adding a safety (either low or high pressure) switch to these older A/C style cars?

Which side would be best the high or low side?

There is no easy way to add the safety switch to either side unless there is an inline adaptor. The two copper lines from the compressor (high and low) are about ½" OD so those maybe a bit harder. The line from the "sight glass" and the one from and to the dehydrator/receiver are about 5/16", so maybe these would be a bit easier.

If possible can a safety switch be added in-line at any of these connections, at the "sight glass" or the dehydrator/receiver?

I believe this line would be the high pressure side so it would need to be a "high pressure switch"?  

A quick online search I found a few in-line adapters mostly for modern A/C lines just not sure if these can be adapted or modified to fit older flare type A/C lines? 

Another alternative is to use one of the charging ports at the compressor to add the safety switch "BUT" this would block the port unless an adaptor is use here.   

Maybe I'm overthinking this just follow the standard "if it ain't broke don't fix it" may be applicable in this case.   

[Cadillac Jack 82]

Honestly when I refilled the 55 I had them do a leak test.  They found a loose fitting and tightened it up.  After that there were no more leaks and they filled her up with the 5 lbs needed.  Wow what an amazing AC system!  Kept me cool as a cucumber in 107 degree heat!  R-134a in the A6 systems can't do that.  I'd just do a UV dye test on the system while charging.  Also what condition are your rear vent boots in?  I know I had to use some silicone to seal a few cracks as those boots are unobtainium.

["Cadillac Kid" Greg Surfas 15364]

As to the subject of tapping into either the high or low side, fittings are available to tap into the refrigerant lines with a short extension of tubing and a 1/4" flare connector. That would give you access to the system.
That said, and to get right to the point, if the system is short o refrigerant, the first thing you would notice would be a decrease in cooling capacity. The next step would be to check the site glass . bubbles, short. Clear glass, full of refrigerant( or at least to that point in the system).
You typically have two sources of refrigerant leakage. 1. The tubing and fittings of the system and a thorough leak check of a pressurized system with an electronic leak detector will assure you of a tight system.
2. The compressor seal. BEFORE STARTING AND CHARGING THE SYSTEM, be sure and turn the compressor (outer clutch plate) over at least 25 or 30 times to get the oil circulating in the compressor and to the seal.
As you yourself intimated, if the engineers who designed this system thought a high or low pressure safety was necessary they would have (in those days, overkill was the norm) included them.
Greg Surfas

["Cadillac Kid" Greg Surfas 15364]

here is an example of a line tap

["Cadillac Kid" Greg Surfas 15364]

try again

[J. Gomez]

Honestly when I refilled the 55 I had them do a leak test.  They found a loose fitting and tightened it up.  After that there were no more leaks and they filled her up with the 5 lbs needed.  Wow what an amazing AC system!  Kept me cool as a cucumber in 107 degree heat!  R-134a in the A6 systems can't do that.  I'd just do a UV dye test on the system while charging.  Also what condition are your rear vent boots in?  I know I had to use some silicone to seal a few cracks as those boots are unobtainium.

Tim,

I know we are going to hear and see this word "unobtainium" more often in this forum as times goes by.     

[J. Gomez]

As to the subject of tapping into either the high or low side, fittings are available to tap into the refrigerant lines with a short extension of tubing and a 1/4" flare connector. That would give you access to the system.
 

Greg,

What my research found was two possible solutions to add a safety pressure switch to this system (see pictures below), one in-line while the other an add-on to the R12 service port on the compressor.

The add-on seems to be the least intrusive method but not sure if the R134a fitting can be replace with a R12, I may need to do a few more researches.

That said, and to get right to the point, if the system is short o refrigerant, the first thing you would notice would be a decrease in cooling capacity. The next step would be to check the site glass . bubbles, short. Clear glass, full of refrigerant( or at least to that point in the system).
 

Agree that is the visual check as described on the Service Manual.

You typically have two sources of refrigerant leakage. 1. The tubing and fittings of the system and a thorough leak check of a pressurized system with an electronic leak detector will assure you of a tight system.
2. The compressor seal. BEFORE STARTING AND CHARGING THE SYSTEM, be sure and turn the compressor (outer clutch plate) over at least 25 or 30 times to get the oil circulating in the compressor and to the seal.
 

Thanks for the tips above.

So far I have pull vacuum on the system and it held vacuum for well over 2 hrs, and a pressure test at around 30 psi also held pressure over a few days.
I will also be checking with an electronic leak detector once I get a few pound in the system since there are multiple connections all around, just to validate.
Running the compressor is something I have yet to do but will do shortly. I still need to make minor adjustment to the fast idle-speed up control so that would give me time to get the compressor going.

As you yourself intimated, if the engineers who designed this system thought a high or low pressure safety was necessary they would have (in those days, overkill was the norm) included them.
 

I'm not sure if the pressure safety switches were made available on any A/C systems of this era.

I have done a few electrical modifications to the A/C control unit since the original layout was overwhelming the load on the ignition switch. If this design was engineered back them with their views of "if the ignition switch fails no problem just get a new one", today is not an option we can afford to have it failed.

So that engineered methodology got me thinking "how to safeguard my compressor", and thus my questions for this topic.

Thanks for your feedback.

["Cadillac Kid" Greg Surfas 15364]

Commercial AC and refrigeration systems had low and high pressure controls from their infancy but those were intended for cycling the compressor.
Greg Surfas