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1969 LIMO A/C QUESTION

Started by 1969cadillac, October 08, 2021, 05:01:35 AM

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1969cadillac

Hello out there i have finally reinstalled the evaporator back into my 69 limo ! what a job ! took just about all day!

Q. as regards the bulb from the TX valve where it is clamped to the top outlet of the evaporator - pls see pics attached - should i just cover the BULB with the black sealant stuff OR should i bunch those excess line coils up too and cover the whole lot with the black stuff?? i just dont want to upset the operation of this thing!

Q. The other line from the TX valve - i have bunched the excess coils together and put a cable tie around them ..is this ok to do? i can always undo it!

thanks ! , Murray Mules


"Cadillac Kid" Greg Surfas 15364

Murray,
In regards to your question regarding the thermal bulb, it should be covered (by itself) in "the black stuff". Murry, does this Limo have a rear unit as well?
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

1969cadillac

Greg the limo does have the rear unit and i have spent countless hours restoring it !! Pls see pics attached ! Dont know if you remember but i was the man who started posting about 6 months ago with the prob where a stupid AC bloke blew up my  front evap up and i have finally got around to fixing it! Q. i guess the other coils wrapped up and tied with the cable tie will be ok? Thanks for all your help Greg - you are very knowledgeable sir .  Murray Mules

"Cadillac Kid" Greg Surfas 15364

Murray,
I don't want to sound negative, but without a POA on the front or the rear systems, the pressures will fluctuate independently, and I really would like to hear how the system works when you are finished.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

V63


The 'bulbs' are there to sense the temperature of the line, specifically to keep the evaporator from freezing. The black goop is to keep the area insulated from surrounding influences. The factory gooped both the components. Yes you can coil and tie the capillary tubes of coarse realizing they are fragile and avoid kinks. I might 'try' and keep the coils near the bulb and within the goop, just For better appearances .


All series 75 (equipped with AC ) had dual air, after and including 1957 models.

I have had both a 1968 series 75 and a convertible. The convertible I eliminated the POA and had excellent results.

I also modified the blower motor  to a 1977 version to increase the velocity of the discharge. It had a wider and more efficient squirrel cage. I was pleased with that noticeable improvement.

I did not use 134a .

What climate do you reside?

"Cadillac Kid" Greg Surfas 15364

Just to follow up, As V63 said, the thermal bulbs from the TX valve are filled with a specific refrigerant for the type of refrigerant used in the system (you did not say what refrigerant you are going to use), and they sense the temperature of the suction line, leaving the evaporator.  The temperature of the bulb results in a pressure to the TX valve, and the valve "compares that temperature to the pressure it receives from the external equalizer line (the small line that goes from the evaporator to the TX valve.  The purpose of the expansion valve control is to release enough, and not too much refrigerant to result in refrigerant leaving the evaporator with an 8-12 degree "super-heat".  That means all the refrigerant has bee evaporated and the return gas has heated 8-12 degrees above it's evaporating temperature.
This ensures all the refrigerating effect in the refrigerant has been utilized and the gas returning to the compressor is "liquid free".
All that said, the Thermal Expansion Valve (TXV) is selected for the refrigerant used in the system so that the bulb charge and the pressure springs inside the valve, as well as the valve orifices and needle valves can accurately control said super-heat. Using the wrong valve for the refrigerant used in the system results in sloppy operation and can lead to flooding back (and endangering the compressor) or throttling too much and not feeding enough refrigerant for the load.
Now that is typically all you need in a stationary refrigeration system with a constant speed motor, but early on the Frigidaire (later Harrison) Engineers determined that with the vastly differing engine and thus compressor speeds in an automobile they needed something to help stabilize their systems.
Enter the hot gas bypass, soon upgraded to the infamous P.O.A valve to keep the pressure in the evaporator above the point at which it's temperature would go below 32 degrees and freeze the moisture being wrung out of the air passing over the evaporator coil.
The combination of TXV and POA resulted in a stable system that was continuously de humidifying the air being circulated and controlling the air leaving temperature to 34-36 degrees, so the Automatic Temperature control ATC would function correctly, delivering constantly dehumidified and reheated air to the cabin to maintain a cabin temperature as requested by the user.
With the dual systems the compressor could count on receiving equal pressure/temperature return temperatures from both, so it drew evenly from both. By removing the POA from both you have severely restricted the operation and essentially negated the ATC's authority to control temperature. If just cold is the desired effect you can probably get it, but temperature "control" becomes quite "iffy".
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

1969cadillac


Greg you obviously KNOW this system very well .....  i am going to use 134a refrigerant. After reading your post i now have some idea of how it works . I am tempted now to get new POA valves for both FRONT and REAR systems !. it sounds like it would work ok with just the rear POA BUT will work better if BOTH POAs are in the system! I dug out my GM master parts book  - it states that he Front one is  GM 5910594  and the Rear is GM 5910603 . It looks like i can prob get a front one as long as it is 134a compatible ...but the rear  one as it was prob only used in the 75 series  may be a prob! Q. would the front POA work on the rear system? i wonder what is different about it ? My limo already had the front POA upgrade kit added when i bought the car - the rear had the orig POA valve fitted ..i have been trying to find it in my parts "mess" - but cant locate it as i wanted to compare it to the old front unit off my old  deville coupe to see what is different about them! Thanks , Murray Mules



Quote from: "Cadillac Kid"  Greg Surfas 15364 on October 09, 2021, 11:55:54 AM
Just to follow up, As V63 said, the thermal bulbs from the TX valve are filled with a specific refrigerant for the type of refrigerant used in the system (you did not say what refrigerant you are going to use), and they sense the temperature of the suction line, leaving the evaporator.  The temperature of the bulb results in a pressure to the TX valve, and the valve "compares that temperature to the pressure it receives from the external equalizer line (the small line that goes from the evaporator to the TX valve.  The purpose of the expansion valve control is to release enough, and not too much refrigerant to result in refrigerant leaving the evaporator with an 8-12 degree "super-heat".  That means all the refrigerant has bee evaporated and the return gas has heated 8-12 degrees above it's evaporating temperature.
This ensures all the refrigerating effect in the refrigerant has been utilized and the gas returning to the compressor is "liquid free".
All that said, the Thermal Expansion Valve (TXV) is selected for the refrigerant used in the system so that the bulb charge and the pressure springs inside the valve, as well as the valve orifices and needle valves can accurately control said super-heat. Using the wrong valve for the refrigerant used in the system results in sloppy operation and can lead to flooding back (and endangering the compressor) or throttling too much and not feeding enough refrigerant for the load.
Now that is typically all you need in a stationary refrigeration system with a constant speed motor, but early on the Frigidaire (later Harrison) Engineers determined that with the vastly differing engine and thus compressor speeds in an automobile they needed something to help stabilize their systems.
Enter the hot gas bypass, soon upgraded to the infamous P.O.A valve to keep the pressure in the evaporator above the point at which it's temperature would go below 32 degrees and freeze the moisture being wrung out of the air passing over the evaporator coil.
The combination of TXV and POA resulted in a stable system that was continuously de humidifying the air being circulated and controlling the air leaving temperature to 34-36 degrees, so the Automatic Temperature control ATC would function correctly, delivering constantly dehumidified and reheated air to the cabin to maintain a cabin temperature as requested by the user.
With the dual systems the compressor could count on receiving equal pressure/temperature return temperatures from both, so it drew evenly from both. By removing the POA from both you have severely restricted the operation and essentially negated the ATC's authority to control temperature. If just cold is the desired effect you can probably get it, but temperature "control" becomes quite "iffy".
Greg Surfas
Quote from: "Cadillac Kid"  Greg Surfas 15364 on October 09, 2021, 11:55:54 AM
Just to follow up, As V63 said, the thermal bulbs from the TX valve are filled with a specific refrigerant for the type of refrigerant used in the system (you did not say what refrigerant you are going to use), and they sense the temperature of the suction line, leaving the evaporator.  The temperature of the bulb results in a pressure to the TX valve, and the valve "compares that temperature to the pressure it receives from the external equalizer line (the small line that goes from the evaporator to the TX valve.  The purpose of the expansion valve control is to release enough, and not too much refrigerant to result in refrigerant leaving the evaporator with an 8-12 degree "super-heat".  That means all the refrigerant has bee evaporated and the return gas has heated 8-12 degrees above it's evaporating temperature.
This ensures all the refrigerating effect in the refrigerant has been utilized and the gas returning to the compressor is "liquid free".
All that said, the Thermal Expansion Valve (TXV) is selected for the refrigerant used in the system so that the bulb charge and the pressure springs inside the valve, as well as the valve orifices and needle valves can accurately control said super-heat. Using the wrong valve for the refrigerant used in the system results in sloppy operation and can lead to flooding back (and endangering the compressor) or throttling too much and not feeding enough refrigerant for the load.
Now that is typically all you need in a stationary refrigeration system with a constant speed motor, but early on the Frigidaire (later Harrison) Engineers determined that with the vastly differing engine and thus compressor speeds in an automobile they needed something to help stabilize their systems.
Enter the hot gas bypass, soon upgraded to the infamous P.O.A valve to keep the pressure in the evaporator above the point at which it's temperature would go below 32 degrees and freeze the moisture being wrung out of the air passing over the evaporator coil.
The combination of TXV and POA resulted in a stable system that was continuously de humidifying the air being circulated and controlling the air leaving temperature to 34-36 degrees, so the Automatic Temperature control ATC would function correctly, delivering constantly dehumidified and reheated air to the cabin to maintain a cabin temperature as requested by the user.
With the dual systems the compressor could count on receiving equal pressure/temperature return temperatures from both, so it drew evenly from both. By removing the POA from both you have severely restricted the operation and essentially negated the ATC's authority to control temperature. If just cold is the desired effect you can probably get it, but temperature "control" becomes quite "iffy".
Greg Surfas

V63

#7
Here is an image of the POA elimination kit.
There is a direct relationship between pressure and temperature, and the switch in the kit turns off the compressor when a certain Low pressure Is met, let's say 23 psi. This would also represent the evaporator temperature too. The idea is to keep it from becoming a block of ice in humid conditions. As soon as the compressor shuts off the pressure increases until the switch tells the compressor to turn on again. This is called cycling and has been an industry standard since 1977 (with cadillac). It's both simpler and very effective vs prior systems of STV POA and VIR

The problem today with the original  system as designed, is the parts are obsolete and the refrigeratant is obsolete. And I won't go into the poor quality of rebuilt components.

The kit allows for cold 🥶 air with MUCH less complexity.