Automotive Air Conditioning Information Forum (Archives)

Provided by

We've updated our forums!
Click here to visit the new forum

Archive Home

Search Auto AC Forum Archives

1978 Cadillac Fleetwood R134A Conversion with a few Questions Pages: 12

fleetwood472 on Sat August 19, 2006 7:10 PM User is offline

Year: 1978
Make: Cadillac
Model: Fleetwood
Engine Size: 425
Country of Origin: United States

I know this post has been asked many times but I am going to start converting my 78 cadillac fleetwood over to r134a. Right now it has r12 and the compressor is locked up. I am going to be buying a delco compressor, and new accumulator. The system will also be flushed. My question is what else would need to be changed to make this system run efficiently with r13ra? I have been looking at also changing over to a new condensor that would work best with r134a. Is there any out there that anyone would recommend? Also what about the orifice tube? I have heard some recommend ford blue ones. What do you think about this? If anyone has any advice or input I would greatly appreciate it. Thanks - Justin

k5guy on Sat August 19, 2006 7:56 PM User is offline

Change the condenser. It will really make a difference.


Send me e-mail

NickD on Sat August 19, 2006 9:40 PM User is offline

I had that same car some 25 years ago, recall driving it through the Dakotas in 125*F weather and was cold inside. I recall pulling out the entire ATC programmer, climate control and all the sensors as my system would lock up in full heat position. Was only a one transistor circuit, cleaned all the gears, and had a dirty temperature control pot. Can't quite remember the AC control system, keep on confusing that car with my 73. One of them and I think it was the 78 had a thermal controlled cycling switch on the right side of the firewall that would cycle the compressor, course looking at it would refresh my memory in a second. Did have the shop manual and every piece of the AC electrical diagram was on it, matter of fact the entire vehicle electrical system was on one large color coded schematic, color of the wires on the circuit matched those in the car. That was a nice touch back then. Was one of those send in four bucks for the shop manual deals.

This system had a fan clutch, that has to be good, 85 amp alternator, and plenty of AC reserve, feel it should adapted well to R-134a, wouldn't fool with the orifice and charge to about 90% R-12 capacity, definitely need a new R-134a compatible accumulator, the adapters with a HPCO switch attached, would go with BVA-100 oil. If your old compressor seized, would be reason alone to go with a new condenser. The radiator in my car was crap rotting out after three short years, got a bit tired of how GM was cheapening this stuff up, would replace that too, can't recall the name anymore, but did get an aftermarket that lasted a long time.

How are your rear disk brakes with the parking brake function, mine drove me crazy on this car. Real crazy system, pumping the parking brake pedal was the way they self adjusted, but the pistons would never ratchet the way they were suppose, would just rock back and forth, and as the rear pads wore, the service brake pedal would go to the floor. Had to pull the rear calipers apart to make the adjustment, many many times. Cadillac had no cure for this problem, thought about switching back to drums off a DeVille.

CorvairGeek on Sun August 20, 2006 4:01 AM User is offline

Did my friend's beautiful '77 Deville this summer. New Evaporator (from Tim) A6 (it does cycle on a temp thermostat) with new double lip seal, GM orifice tube, and original condenser. System was squeaky clean, so used DEC PAG from Tim. Low 40s with 134a (90%) in the high 90s here in the high desert (new fan clutch). He was thrilled. A lot to be said for an over engineered system. I had forgotten how smooth and quiet A6s are.


CorvairGeek on Sun August 20, 2006 4:06 AM User is offline

He did new hoses locally too. Only the liquid line was reusable, and this car is in truly amazing condition. I don't know if the original leaky fittings would hold 134a for any time at all, they were lucky to hold R12 (I would have kept it R12 myself, but it was his choice).


NickD on Sun August 20, 2006 8:20 AM User is offline

Always question whether the Fleetwood or the DeVille was the better car back then, feel it was the DeVille as they didn't rust out as quick as the Fleetwoods did. My 73 had nothing but bare sheet metal on the inside of the door and fender panels if you can believe that, did a complete undercoating, but still rusted out. But the interiors wore like iron, darn near needed a crane to remove the door panels. The 73 Fleetwood was a huge car, much larger than the DeVille of that year, but not much difference in 78. Least the 78 had a Cadillac engine, in 81 they were using a Chevy 350. My 78 had a 2.22 rear end ratio, could easily run up to 65 mph in first gear without revving up the engine, but got pretty close to 20 mpg.

Loved those touch tuning bar radios, I put mine on the bench and just clicking it on drew over 5 amperes. Delco was still using the DS 501 germanium class A transistors in that radio pulling the same current whether the volume was off or at maximum which wasn't that loud. I got rid of those and installed two 20 watt solid state amplifiers only drawing 3/4 ampere at normal listening levels. Added an under dash cassette player with a relay that would switch over the amplifier whenever a cassette was installed and some decent speakers. Sounded more like what you would expect from Cadillac.

Still pleased with my 92 DeVille, had that car about seven years now, proves that GM can do it, but looked at later models and all downhill again.

Chick on Sun August 20, 2006 8:29 AM User is offlineView users profile

Use the "FORD" blue O tube..Your pressures will be closer to R12 pressures in my experience
Hope this helps..

Email: Chick


Freedoms just another word for nothing left to lose

NickD on Sun August 20, 2006 8:54 AM User is offline

Wish I kept that 78 factory manual for more reasons than one, had a beautiful description of the TH400 transmission with all colored drawings, and that project is still on my list. Thought there was some kind of low pressure cut off switch, but as CorvairGeek confirmed, definitely had the evaporator thermostatic switch that controlled the cycling, kind of like saying the heck with pressures for the conventional cycling switch. Recall playing with that switch, had two adjustments, one was for the low temperature cutoff point, the other interactive with the first determined the high temperature cutoff point.

My thoughts with this system was to keep the refrigerant flowing as pressures like in the computerized Cadillacs are not nearly as important, but only a 10% difference in the two orifice area sizes. Suppose a guy could flip a coin.

fleetwood472 on Thu August 31, 2006 12:10 AM User is offline

Thanks for the info guys. So what would be recommended to change? The condensor, compressor, accumulator and hoses? Who do you guys recommend for the hoses? How does it work do I send them my old ones and they use them as a template to make r134a compatable hoses? Also for orifices should I use the ford one or is it not a huge difference? Thanks - Justin

NickD on Thu August 31, 2006 7:31 AM User is offline

Seems like GM knew how to make good radiators, condensers, evaporators, and heater cores in the 50's and early 60's, then each year were made thinner and cheaper. had a lot of problems in my 78 Fleetwood that really teed me off with these components and would replace them just on that basis alone. Took them to my favorite radiator shop back then. an excellent older gentleman, honest, hardworking that told me, there just isn't anything there left to repair. If I repair one leak, you will get ten more in different places. Would be tempted to use a parallel flow condenser, actually you have a 472 jammed in that tight engine compartment with smaller holes, really gets hot compared to the older ones. If your hoses are 28 years old, reason enough to replace them with barrier hoses.

The purpose of the smaller orifice would be to increase low side pressures, just don't recall the low pressure circuit in this vehicle to determine whether this will be a problem or not, if Chick has experience in this, would follow his advice. Also hear there is a neoprene replacement for that rear engine rope seal, that would be a welcomed addition.

Chick on Thu August 31, 2006 7:55 AM User is offlineView users profile

Originally posted by: fleetwood472
Thanks for the info guys. So what would be recommended to change? The condensor, compressor, accumulator and hoses? Who do you guys recommend for the hoses? How does it work do I send them my old ones and they use them as a template to make r134a compatable hoses? Also for orifices should I use the ford one or is it not a huge difference? Thanks - Justin

Send an e-mail to the guys at and get a price on everything all at once. You can ship all your hoses to them, and they rebuild them with barrier hose. They can also give you a price on all the parts you need. If you change the condenser, you should go with a parallel flow condenser, which would involve new hoses anyway. A system flush will be needed if you keep your condenser and evaporator to remove the old mineral oil. can provide you with either PAG 150 DEC or BVA Auto 100 ester, both will work find, and I recommend the ford blue O tube on "all" GM retrofits. But the choice is yours...Hope this helps..

Email: Chick


Freedoms just another word for nothing left to lose

fleetwood472 on Fri September 01, 2006 11:40 AM User is offline

Thanks for everything guys. I am looking at parts and am thinking about basically replacing everything but the evaporator core. Would you recommend changing the evaporator core? Any other upgrades you guys would recommend? Do you think if I replaced the condensor with another stock condensor the system would probably operate efficiently with R134A or should I not risk it and go with a parallel flow condensor? Thanks - Justin

fleetwood472 on Wed January 19, 2011 4:35 PM User is offline

fleetwood472 on Wed January 19, 2011 4:38 PM User is offline

Well i'm resurecting this post haha. I'm finally getting ready to do an R134 retrofit. I havent gotten to the A/C system yet because I just swapped in a new transmission and replaced the 425 with a 472 and custom EFI. Now that I get ready to do this swap i'm thinking of replacing the locked up A6 with either a V5 or V7 compressor. Does anyone have recommendations for which V7 and V5 compressors that have a similar mounting tab configuration to replace the a6? I know i'm going to have to fab some brackets but i'm just looking for the best setup to use as far as mounting ears and I know that there are multiple configurations of V5 and V7's. Thanks - Justin

bohica2xo on Wed January 19, 2011 10:58 PM User is offline

Run the biggest parallel flow condensor that will fit.

The V7 is an excellent choice to replace the A6 in a car like that. The original POA valve can be removed, since the V7 handles that job internally.

I would keep the TXV valve on the evaporator.

You can use THIS V7 Compressor, and if you need a V belt pulley you just swap the V belt pulley from a V5. AC Kits can probably assemble a V7 with a V5 "V" belt clutch for you.

A V7 with a TXV matches up with the OEM design for that car.

"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

NickD on Thu January 20, 2011 6:37 AM User is offline

See I posted where I had my 92 DeVille for six years, make that eleven years now, ha, thought I was slow in getting things done. 472 won't be any worse than that 425, since the 425 is an under bored 472 with oversteering in this car, put this car second to my old 67 Mustang as one of the worse winter cars I had. Did have limited slip, but with all that weight on the front tires, even with a little snow on the ground, both rear wheels would just spin like crazy. Had to add about 300 pounds of sand bags in the trunk to drive it in winter.

The 1976 was the last of the Fleetwoods that was well balanced, in 77 was a panic to get better fuel economy greatly reducing the size of the car, took most of the weight off the rear wheels where it was needed. Sway on the highway was yet another problem I couldn't resolve, constant correction on the steering wheel. Also recall problems with the automatic climate control, had the kids in the car on a very hot summer day when a thunderstorm kicked up when the climate control decided to kick out 195*F air. Thank goodness we were only ten miles from home, but were pretty well baked when we got there. Did pull the entire ATC controller, all electro-mechanical with one transistor, mostly all dried up grease, recall taking the temperature control potentiometer apart for cleaning, wiper wasn't making good contact.

Recall that the blower switch with resistors and vacuum mode switch were servo driven that also needed cleaning and relubrication, what was nice with the aid of a vacuum pump and a 12 V power supply, could see everything in action as opposed to these microcontroller contraptions of today.

What POA valve, this car used that thermostatic switch, compressor did cycle. Recall on the rear page of the shop manual, the entire MVAC system was shown in schematic form along with the entire rest of the vehicle on one single fold out page. All you see today is blocks with empty spaces on the inside.

Did test drive a new 81 DeVille, switched to a Chevy engine, recall the acceleration was worse than a 54 six cylinder Chevy with a two speed Power Glide. Power had no meaning in that name. That was the time I did something entirely against all my principles, switched to Japanese made cars.

Anyway, have fun.

fleetwood472 on Thu January 20, 2011 11:18 AM User is offline

Thanks for the info bohica2xo. Looks like that case style should go in pretty well without too much modification to the brackets. Now for another question. I hear the V7's are pretty dependable. Do you think it would be a huge risk to toss a good used one on or should I just by new? I've heard conflicting stories haha. Also should I run a variable oriface valve or just stick with the stock TXV? As far as condensors i've been told that the stock one should be big enough. If anyone has one they'd recommend let me know because my stock one is shot anyways and i'll be replacing it. So I might as well find one that is optimal for my setup. I'm going to run a 2 speed fan out of a 90's lincoln that i'll be adapting. My ECM will know when the A/C clutch is engaged so it will automatically kick the fan in to hopefully cool the condensor enough. I'm sure this will be better than the current clutch fan.


Ya i've been pretty lazy with this car haha. It's pretty much been sitting in storage the past few years. Back in 2000 I swapped an analog EFI system from a 77 eldorado into my fleetwood and it ran great. I'll never go back to carbs. A buddy of mine had a 76 fleetwood and it was a dog compared to my fleetwood after I put the EFI on it. And thats even with a 2.28 rear end in it! I havent really had a ton of problems with the car. Maybe i've been lucky. I finally replaced the crappy stock alternator with a 140 amp CS144 from a 95 roadmaster. That really made a difference as far as electrical draw. The window motors are alot faster now to. It was practically bolton. Hopefully i'll get this thing up and running right by the summer! If not i'm sure you'll see another post from me about it in 3 more years hahaha.

So basically with this system i'm replacing the compressor, condensor, accumulator, orifice valve and replacing the hoses along with flushing the evaporator core. Any advice for plumbing the hoses? I figure's i'd grab about a foot long pice of each hose coming from a V7 in the junk yard. Then once I take the hoses in to an A/C shop to put new barrier hose on i'll have them use the V7 fittings. Any other advice? I might go through the climate control assmebly and clean up all of the contacts on it cause i'm sure its a little dirty for being over 30 years old. Any advice on where to find the V5 compressor v-belt pulleys? Do you guys know what applications of cars used them? Are there smaller pulley's available and are they needed to get the compressor spinning sufficiently at idle? Thanks - Justin

Thanks - Justin

Dougflas on Thu January 20, 2011 7:01 PM User is offline

Here is a trick I use all the time. Since you're having to manufacture or modify compressor mounting hardware, use a round laser pen to line up the pulleys by putting the laser in one pulley(water pump or harmonic balancer pulley and shinning it into the compressor clutch pulley.

Edited: Thu January 20, 2011 at 7:03 PM by Dougflas

bohica2xo on Thu January 20, 2011 10:47 PM User is offline


The 1985 Cavalier used a "V" belt - V5 compressor with V belt drive

Some other models as well. Just the first one that comes to mind.

You are right, that was one of the CCOT / A6 disaster cars. I saw "472" + "A6", and thought it still had a real system - forgot to check the year of the vehicle itself.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

NickD on Fri January 21, 2011 6:26 AM User is offline

For fleetwood472, the V-7 is a variable displacement compressor that runs all the time with a fixed orifice. Typically, just a high side thermistor is used to shut down the compressor if the pressure range goes beyond 40-430 PSI, but I feel a dual function switch from a Toyota or a Honda should do the same thing. Normally feeds the PCM, so other things can kill compressor operation like an over heating engine or rapid acceleration. But if you have brains, can switch your climate control to economy and do the same thing.

Have a V-5 in my 04 Cavalier, a bit annoyed that it kicks on the compressor, provided the high side pressure is at least 40 psi if I switch the mode switch to either the recir or the defrost positions, but in freezing temperatures when the high side is below 40 psi. They also put on an AC clutch switch, but it is bypassed by the mode switch. Was going to change that as my little wife forced the mode switch in subzero temperatures and bend the cable that operates the mode door. No vacuum in this car except one actuator for the recir door, a speedometer type foot long cable operates the mode door. But after looking at it, would break it trying to remove the electrical switch part of that switch. Is electrical, vacuum, with a swinging lever to operate the mode door.

Was a TSB on this car where the foam on the mode door falls off jamming it so if forcing the mode switch can bend that cable. But for some peculiar reason I haven't determined yet, on very cold days, that mode door jams. Always that way since new. Took the entire upper dash apart, the foam was still there and in very good shape, but was ready to fall off. As I suspected, held in with double sided scotch tape that is kind of stupid for a door that sees a 30 to a 195*F temperature range. Put it back on using weather strip cement.

I learned that door foam only seals off the dash vents and only in the defrost mode, in all other modes, a little air sneaks by like in floor, can feel a very slight breeze on the dash vents, so what! But even on a subzero day, just driving the car about 8 blocks, enough heat to free that door. If it wasn't such a bitch to remove, would have pulled it and trimmed off another 1/32" from each end. Feel the coefficient of expansion between the housing and that door is different causing that door to jam in subzero temperatures. After the car warms up a tad, that door is perfectly free and mode switch is effortless to turn. Always problems, the cable was looped before it got into the jacket. Straightened the old one out, but spend 13 bucks anyway for a new one. Wasn't very easy to change. Found thousands of others had this same problem. But the V-5 in this car with R-134a is excellent. Cools the car down in about a block after it sat in the hot sun.

fleetwood472 on Fri January 21, 2011 2:19 PM User is offline

Awesome idea! I'm definitely going to try this one when I work on making mounting brackets and lining up the V7! Thanks!

Thanks alot when I go to the salvage yard i'll keep my eyes out for some older cavaliers. Do you think those cheap rental clutch pullers from autozone would work to pull the clutch and pulley assembly off of a donor?

Thanks for the info. I remember my brother's 96 9c1 caprice would kill the power to the compressor clutch when you hammered the throttle. The ecm i'm using in my cadillac is out of a 91 transam. I'm going to see if the ECM has an option where I can kill the power to the compressor clutch during hard acceleration. I dont see why it wouldnt since I have the VSS enabled to it and am using a TPS.

So I know its been asked in previous of mine but now since I am going to use the V7 compressor and not the A6 should I stick with the stock orifice valve or use the ford blue? Any ideas are appreciated. Also any ideas for doing a mock setup with the plumbing? I figured i'd grab some junkyard hose assmblies from V7's and V5's then sort of piece them together to run to an aftermarket parallel flow condensor. I'm just trying to figure out how to get them to keep shape if I sent them in to be redone by ACKITS. Any ideas? This part is pretty new to me. NickD, any ideas on the best application vehicle to grab the solid lines from the back of a V7 to use for my 78 fleetwood or what would be similar as far as bends in the hardline? Just trying to get some ideas. Thanks - Justin

Back to Automotive Air Conditioning Forum

We've updated our forums!
Click here to visit the new forum

Archive Home

Copyright © 2016 Arizona Mobile Air Inc.