News:

Due to a technical issue, some recently uploaded pictures have been lost. We are investigating why this happened but the issue has been resolved so that future uploads should be safe.  You can also Modify your post (MORE...) and re-upload the pictures in your post.

Main Menu

1970 Cadillac R134 back to R12 conversion

Started by Scot Minesinger, July 24, 2019, 04:13:17 PM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

Scot Minesinger

R134 is going away (please no comments about why)  R12 works better in our 1950'-s thru 1980's Cadillacs.  I have owned my 134 Robinaire model 34788 for about 7 years now and have made the money on it.  It is out of warranty.  I still need to be able to work on r134 cars.

I'm ready to buy a new Robinaire 34788 and devote it to r12, thus having two machines, one for each refrigerant.  Then I would convert my 1970 SDV back to r12.  Many people that I help work on their ac have retained the r12 systems or want to convert back, so the 4k hit it takes to get this set up would pay itself back over some time as the original 34788 did 7 years ago.

In calling Robinaire, using r12 in a new model 34788 made for r12 would void the warranty.  They did offer verbally that r12 would probably be fine in their 34788 machine.  However, I could use my 7 year old machine for r12 (converting it over), and then buy the new machine and keep it for 134 and retain the warranty.  On the original 34788 unit, never suffered a warranty issue.

Converting from r134 to r12, it is understood that all components must be clean and void of r134 and r134 (PAG150) oil.  When I converted r12 systems to r134, I flushed the evaporator and condenser, replaced the rubber hoses, replaced drier (Or VIR), removed compressor drained oil, flushed it, added back the r134 oil and reinstalled.  The expansion valve was also flushed. 

Is the degree of conversion back about the same or is r12 less tolerant than r134 to a contamination with the other refrigerant or refrigerant oil, no matter how slight?  This question applies to the cars and the 7 year old 34788 unit.

I'm on the fence about just using the new 34788 for r12 and risk warranty issues.  However, if there was a warranty, it may be not obvious for the tech to know I made the switch unless they checked the tank.



Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

"Cadillac Kid" Greg Surfas 15364

Scott,
Every chemical through its reaction with system components leaves it's "fingerprint". So, yes they will be able to tell it R-12 was used in the device.
In regards to replacing 134a with 12 in a 12 system cleanliness is next to ...you know what.  When I found 134a unsuccessful and went back to 12 I couldn't get back to 100% capacity until I fully dis assembled the system, thoroughly flushed out all the "nooks and crannies", replaced the o-rings Diss assembled the VIR and the compressor to get all the residual "stuff" out and then with a new dryer, new compressor seal and correct seal break in I got back to where I started and that has been some 15 years with no issues on my 3 daily drivers.
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-

Scot Minesinger

Thanks Greg, what I thought but your confirmation is reassuring.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

bcroe

Those systems are so troublesome compared to say, a fridge or even
a house cond.  I suspect the efficiency is awful, but that is a lot less
important than their ability to have the capacity to quickly cool down
a car.  Anybody know numbers on R12 capacity (tied to rpm) or
efficiency? 

All the maintenance issues I believe are related to the rotating seal,
inferior hoses, and so many other joints.  Recently working with 5 of
the latest mini split heat pumps to heat and cool 2 buildings, I am
very impressed with the superior technology.  In particular they are
driven by so little energy, which is electricity.  Wondering if a contained
car system could avoid the earlier problems?  Electric load would be a
problem, perhaps initial cool down capacity would be another.  How do
electric cars do it?  Bruce Roe

J. Gomez

Quote from: bcroe on July 25, 2019, 12:36:17 PM
How do electric cars do it?  Bruce Roe

Bruce the A/C compressor has a DC motor and it runs from the high voltage DC power plan, similar to hybrid vehicles as well.  ;)

HTH
J. Gomez
CLC #23082

"Cadillac Kid" Greg Surfas 15364

a. Compressor:  The compressor is the mechanical “heart” of the refrigeration system.  Its function is to take the refrigerant vapor from the discharge of the evaporator coil and compress the refrigerant to a higher pressure and temperature so that it can be re condensed into liquid and the cycle repeated. The Frigidaire Model A-6 compressor, the one used exclusively on all Cadillac AC systems through 1980 is a 3 cylinder, 6 piston double acting compressor displacing 12.6 cubic inches.  What this means is that each rotation of the compressor pumps 12.6 cubic inches of refrigerant vapor.  The actual refrigerating effect of R-12 (and all other refrigerants) is listed as BTU’s per pound of refrigerant circulated, so the actual conditions of pressure and temperature at which the refrigerant vapor enters and leaves the compressor must be taken into account when figuring the actual “cooling” capacity of the refrigerant compressed by the compressor.  The nominal rating of the A-6 compressor is 27,000 BTU’s at 2000 RPM.

  The compressor is belt driven by the automobiles engine with a clutch to disconnect the compressor when cooling is not desired. Typically the drive ration of the compressor to engine speed is about 1.48:1. This means for every 100 times the engine turns over, the Air Conditioning compressor rotates 148 times.  That relates to a compressor speed range of about 1000 RPM at idle to 6000RPM at 100 MPH.   The smaller the diameter of the compressor driven pulley, the faster the compressor will rotate at any given engine speed.   


Years back a parts listing of a “heavy duty, high capacity” “ambulance” A-6 compressor was essentially one with a smaller (4.6 inch diameter vs. 5.0 up to 5.563 inch diameter for the passenger car).  Most of the alternate sizes have not been available for several years The nominal rating of the A-6 compressor is 27,000 BTU’s at 2000 RPM.  What this means is that at 2,000 compressor RPM, 1,350 engine RPM or about 25 miles per hour, the compressor will pump enough refrigerant vapor to result in a system cooling capacity of 27,000 BTUs, or about 2 “tons” of cooling. 

This was determined to be the “average” summertime heat load from sun and outdoor temperatures on the roof, glass and sides of the vehicle, as well as the occupants.
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-

TMoore - NTCLC

First, I agree that using R-12 in a R-12 system is the way to go.  The price for R-12 was an issue for a couple of years, but it quickly settled into a price range that made sense to keep an R-12 system running R-12.  I have never personally seen a conversion that would adequately cool a car in triple digit heat with the same effeciency as the original R-12 (I have read that they exist, but never personally experienced one).

Second - I always found it amazing that you can get into a hot (120 degree +) car, start it up and engage the A/C and within minutes have 35 degree air discharging from the vents.  I am lucky to get a 20 degree differential out of my home A/C, but the car will pump icicles out of the vent.  Most people would think that approx. 2 tons of A/C to cool a car is overkill, but the engineers did the math on the heat gain, and they pretty much got it right.  I typically run my A6 compressors on max during the hot Texas summers, but if I am on on a highway drive, I will often find that I need to ease out of max or risk getting a bit too cool.

bcroe

With an output of 27,000 BTU/hr, the Coefficient Of Performance
could be calculated if we knew the horsepower.  A lot of horses at
2000 rpm I suspect.  The R410A units here have a COP of near 4,
doing 15,000 BTU/hr with a variable speed, inverter driven, very
quiet compressor.   Looks like it falls short at both the input and
output ratings. 

The 79 Eldo did not use the A6 compressor, used the R4 just like
the Toro.  But the idler bearing in the clutch is the same as the
A6, ask me how I know.  Bruce Roe

"Cadillac Kid" Greg Surfas 15364

"old school" compression refrigeration systems usually run about 1 HP/Ton of refrigeration. That would put the load on the engine at full (AC) load of about 2HP.
Now if you are looking for thermal efficiency an engine driven, condenser in front of the radiator, fan cooled is not the way to go.  On a 95 degree day with outside  air over the condenser the condensing temperature will range from 120 to 160 degrees and above due to the radiant heat of the engine compartment and the radiator.
Current HVAC equipment design for residential and commercial applications can run something like .22 H/Ton of refrigeration. R410a systems have condensers essentially 3 times the size (for the tonnage) of previous generations of  equipment.
As far as "outlet" temperatures, residential and commercial systems have air "diffusers" that actually mix the air in the space with the air coming through the ducts.  The purpose of AC is to provide an even and comfortable temperature in the occupied space, and (actually) 21.6 is the typical design temperature differential, otherwise air coming out of the outlets would drop to the floor and there would be quite a temperature gradient from the floor to the breathing space (approx 5' above the floor).
Since automotive AC systems deliver substantially less than the 400+ CFM/ton of cooling that stationary systems do, the air must be colder to provide adequate cooling. It wasn't until about the mid 70's that Automotive air outlets were starting to be designed for the requisite mixing.
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-

cadman56

A question from someone who knows very little about A/C systems except the wallet greatly suffers when the system goes down.

Why not purchasw a used unit then disassemble and restore to use R12?  Would it be possible to do and at less cost than Scot suggests?

Thanks for your patience.
1956 Cadillac Coupe deVille (sold)
1956 Cadillac Convertible (sold)
1956 Cadillac Eldorado Seville (sold)
1967 Cadillac Eldorado (sold)
1968 Cadillac Convertible (Sold)
1991 Cadillac Fleetwood Brougham dElegance
Larry Blanchard CLC #5820

cadillacmike68

27,000 BTUs.  That more than twice the size of a large window unit and can cool an average house.
Regards,
"Cadillac" Mike

Scot Minesinger

Larry,

I have a used unit, and I will switch it over to r12.  Then I will get a new r134 machine.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

bcroe

Quote from: Scot MinesingerLarry,

I have a used unit, and I will switch it over to r12.  Then I will get a new r134 machine. 

I suppose some components carry a rather inflated price, because
they are officially approver?  When I needed a scale to measure
refrigerant out of a bottle (1/10 oz resolution) I found a postage
scale with identical specs to the industry names, but 1/3 the price. 
Bruce Roe

"Cadillac Kid" Greg Surfas 15364

Scott,
You might consider getting the requisite HFO-1234yf equipment, seeing that every Cadillac for the last 6 or seven years has been so fitted. The refrigerant itself has plunged to about $80.00 per pound in 10 pound cans.
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-

bcroe

Quote from: "Cadillac Kid"  Greg Surfas 15364
The nominal rating of the A-6 compressor is 27,000 BTU’s at 2000 RPM.  What this means is that at 2,000 compressor RPM, 1,350 engine RPM or about 25 miles per hour, the compressor will pump enough refrigerant vapor to result in a system cooling capacity of 27,000 BTUs, or about 2 “tons” of cooling.       Greg Surfas

2 horsepower is 1491 watts.   27,000 btu/hr is 7913 watts.  if these numbers
reflected the situation, the COP would be 5.3. That exceeds any of the systems
I am familiar with, but I suspect the horsepower is way low at that capacity. 

Bruce Roe

"Cadillac Kid" Greg Surfas 15364

Bruce
The technology that went into the early AC systems is over a century old. Functionality was primary goal. Efficiency was something that was a distant afterthought.
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-

bcroe

Quote from: "Cadillac Kid"  Greg Surfas 15364 on July 26, 2019, 04:04:23 PM
Bruce
The technology that went into the early AC systems is over a century old. Functionality was primary goal. Efficiency was something that was a distant afterthought.    Greg Surfas   

Right, I am just trying to understand them and how they compare.  Bruce

TJ Hopland

In a car where does most of the heat load come from?   How much is sun through the windows vs sun on the exterior?  And assuming the same exposure does the exterior load change when the car is moving?  Like does the airflow cool the surface enough that it doesn't soak through and radiate to the interior?
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

"Cadillac Kid" Greg Surfas 15364

TJ,
People sweat and that is why when you are in a breeze it feels cooler, the moisture on your skin evaporates and cools you down.  The heat load of course comes from conduction, convection and radiation. The sun radiates heat to the glass and body panels, the outside air conducts heat to the the body panels, class and outside air inlet, and the heat in the outer panels is conducted to the car's interior.
Insulation in the roof and body panels help slow the heat transfer down , but a heat soaked car takes a lot of cooling to bring the interior components (seats, carpet, glass, dash, etc.) down to a desirable temperature.
Basic heat transfer calculations can be used to determine the amount of heat that is transferred to the interior per each segment (glass, roof, etc.) of the car.
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-