: 1977 Sedan De Ville A/C problem



chris85713
06-22-05, 05:00 PM
I just bought a 77 Sedan De Ville, it looks like it just rolled off the showroom floor and only has 76,000 (verified even!) miles on it.

The first couple of days, the climate control system worked, but blew hot air. It's wearing a sticker that says it was converted to R134 so we had it recharged. It worked fine for a couple of days then started trying for a few minutes then switching to heat from A/C. Now, it's stuck on heat mode.

My regular A/C guy says it's because the sensors don't recognize the R134 and we need to switch it back to R12 at a cost of $450 to $500 dollars. I called the local Cadillac dealer who confirmed that it's not recommended to convert the older models to R134 and changing it back would be a good idea.

Another A/C man (yep, just like dealing with a doctor, I went for a second opinion!) says it will work on R134. He's claiming that the refrigerant has all leaked out and that he needs the car for three days while he puts some dye in it and searches for leaks. He'll also recharge the system once the leak is located.

Can anyone confirm that this system will work on R134? I realize that with the environmental concerns the R134 is better, but this is Arizona and I really need for COOL air to come out of the dash - it's been over 105 degrees every day for two weeks now and heat coming out of the floor vents is NOT making driving a pleasant experience.

Feel free to email responses as well as posting here.....

The Ape Man
06-22-05, 07:28 PM
Whomever recharged your system should have added some dye. That is standard operating practice in shops who actually care if you car repair lasts. Some shops keep dye in all referigerant oil so it is possible that the oil added during the conversion had some dye. Find someone honest who knows how to use Ultra Violet leak detection. With the age of your car I'd suspect the factory crimps where the hoses meet the aluminum tubing. Sometimes the crimps can be carefully cut off and replaced with stainless steel clamps
There are no hi tech sensors on your airconditioning system so that is not an issue. R134A systems require a different style condensor in order to work properly. A 134A conversion on a '77 SDV will work but not as well as the R12.

N0DIH
06-22-05, 08:30 PM
R134a molecular structure is "smaller" than R12, so it is very good at finding leaks and leaking out.

As the Ape said, if you don't do your own work, find someone decent to work with. Way too many mechanics are crooked or just plain don't know and replace stuff that isn't needed (they use your money to troubleshoot your own car) or tell you things to get killer business like R12 sales which are several dollars per OUNCE! Considering the average RWD Cadillac needs 28+ oz, that hurts big time!

chris85713
06-22-05, 09:19 PM
Thanks much guys!


The recharge that was done was by the dealer where I bought the car - who swears that two cans brought it up to full.......

You are also correct on A/C repairmen. The first one I contacted said it won't work on R134 and that he's going to need about $500.00 to convert it back to R12. The second one said he'd be happy to diagnose it, but he needs at minimum two hours @ $72.00 an hour to do that, then a minimum of three days to find the leak......

There is good news, though.....

One of my clients is a retired Cadillac mechanic. He'll be here tomorrow with Dye, an ultra violet light, and four cans of R134. He also said it's useless to check any of that until he's checked the vacuum lines that control the entire system, he said the symptoms indicate that it may have a cracked or loose vacuum line as well. He also said that he should be able to find a leak in 30 minutes or less if in fact it leaked out two cans of refrigerant in 48 hours.

I'll let you know what we find.....

By the way, I do have pictures if anyone would like to see them.

chris85713
06-23-05, 08:35 PM
Here's an update, the mechanic just got here, checked things out and said he's coming back tomorrow......

The R134 charge is full. It did contain green dye, there's not a sign of a leak anywhere. The compressor kicks on, then stops in about 30 seconds. It does make a chattering noise for a couple of seconds when it first comes on. It seems to repeat this about every two minutes. It's still blowing hot air out the floor vents. The mechanical one will be back tomorrow to go further into the system.

Just to double check the mechanical type, what would you suggest next?

cadillacdeville
06-24-05, 02:03 AM
It might have to do with the R134A I think maby it could be causing a problem with the Thermostatic Cycling Switch which opens when the capillary Temp drops below 32degrees and closes when it rises to 45degrees I think that the R134A charge itsn't getting cold enough so nothing is getting to the Evaporator

chris85713
06-24-05, 10:42 AM
So, would you recommend taking it back to R12, or is there another solution?

I really wish I had more mechanical knowledge, I'm getting answers on both sides of the issue, some claim they've converted them and had them work fine, others (including the Caddy dealer and a reputable A/C shop) claim it needs to go back to R12 - unfortunately the budget won't go along with the estimates to convert it back. I'm almost at the point where I actually regret buying a Caddy, even though I've dreamed of owning one since I was in high school!

The Ape Man
06-24-05, 12:26 PM
There is a chance that the refrigeration part of the AC system is working OK but the vacuum controls are not allowing the air to be cooled. The guy who looked at it last says it's full. Did he put a set of pressure gauges on the system and run it?
A few things to ponder:
The pressure readings will tell a whole lot about what is going on.
When the AC is on is does the accumulator (the big alumunum cylinder passenger side near the firewall) tank get very cold?
That system relies on a capillary tube to cycle the compressor. The cycling switch is located near the accumulator and has a 2 prong plug. There is a spring loaded pressure switch inside which is actuated by a silvered colored capillary tube. The tube is clamped right onto the pipe that goes into the accumulator ( you can't usually see this as it is gooked up with black insulation). The accumulator temperature acts on the capillary tube to control the switch. When temp is low, the switch cuts off power to the compressor clutch. You can jump the switch to see if it is cutting off the power. There might also be a low pressure switch in the rear of the compressor. That would be in series with the compressor clutch ground terminal. Again, gauges would tell why it would be cycling.

Back to the air controls. You might try carefully pinching off one heater core hose. That system runs air through the evaporator to cool it off but then cycles some air to the heater core to warm it back up again. If the air mode doors are not working then it could be running too much air through the heater core. There is also a heater control valve located under the hood in line with one heater hose. It could be frozen open.

You will avoid buyer's remorse only by obtaining and reading a factory shop manual.

chris85713
06-24-05, 12:43 PM
>There is a chance that the refrigeration part of the AC system is working OK >but the vacuum controls are not allowing the air to be cooled. The guy who >looked at it last says it's full. Did he put a set of pressure gauges on the >system and run it?
>A few things to ponder:
>The pressure readings will tell a whole lot about what is going on.

He did put a guage on it, hooked it to the low side and pegged the gauge. He claims that's normal pressure for a fully charged system.

Then he pulled a two wire plug that hooks on a sort of square looking box at the back of the engine compartment, passenger side (right behind the silver cannister where they charged it. When he jumpered the two wires the compressor started and stayed on. The system continued to blow hot air through the heater ducts.

cadillacdeville
06-24-05, 02:19 PM
the $450 to $500 to switch back seems very high theres not much to a A/C conversion some O-rings difrent oil and the new 134 what cost the most is the R12 which runs for about $33 dollars for 12 OZ which according to my 77 cadillac service manuel says it takes 3 and 3/4 pounds for a full charge with 10.5 OZ of 525 viscosity oil for the compressor I would check around with some more garages to see what others charge

The Ape Man
06-24-05, 03:18 PM
>There is a chance that the refrigeration part of the AC system is working OK >but the vacuum controls are not allowing the air to be cooled. The guy who >looked at it last says it's full. Did he put a set of pressure gauges on the >system and run it?
>A few things to ponder:
>The pressure readings will tell a whole lot about what is going on.

He did put a guage on it, hooked it to the low side and pegged the gauge. He claims that's normal pressure for a fully charged system.

Then he pulled a two wire plug that hooks on a sort of square looking box at the back of the engine compartment, passenger side (right behind the silver cannister where they charged it. When he jumpered the two wires the compressor started and stayed on. The system continued to blow hot air through the heater ducts.


OK now were are getting someplace. Next question is what happened to high and low side pressures with the capillary switch jumpered?

chris85713
06-24-05, 03:29 PM
The pressure on the low side stayed the same. I didn't see him put a gauge on the high side so I couldn't tell you what happened there.

N0DIH
06-24-05, 04:14 PM
You should see typically 25-30 psi in 80 degree weather low side, compressor on, vehicle doors open system on max (60F). And you should see around 250-350 psi on the high side. If you are seeing high pressure on the LOW side and the compressor is ON, it is way overfilled! Remember, if liquid hits the compressor it will hyrdo lock and break it! Do NOT overfill!!!!

chris85713
06-24-05, 04:22 PM
Thanks for the numbers, but what effect does additional heat have on them? This time of year, we don't even see 80 degrees in the middle of the night unless we're really lucky. Our overnight lows are generally 84 or so, during the day it's been right around 110 for the last two weeks.....


Does the pressure go up or down with additional heat?

N0DIH
06-24-05, 07:57 PM
I will post from home my 94 FWB numbers and those for 85 FWB, that should be close.

They are affected by temp, humidity, baro pressure, etc. Key, doors open on the car.

Pressure goes up with heat. 70 is like 20-25 psi low side, high side is like 125-150. So you can plot a rough graph on that. But wait to actually gauge it for the real numbers.

I picked up a "high/low" gauge for filling freon at Meijers here in town. It "goes both ways". So I have an older low side only gauge and use both, so I can monitor both sides at one time.

Monitoring low side only and judging that as your fill is guesswork at best. The high side is the important side.

chris85713
06-26-05, 02:49 PM
Time for an update.....


Two days at the shop, and a considerably lighter wallet finally got it working, but only in the mornings when it's relatively cool. Once the car sits in the sun for an hour or so we're right back to the same problem - hot air coming through the floor vents. Even the mechanic is confused on this one, he's going to do some research over the weekend and wants it back Monday morning. Any ideas?

N0DIH
06-26-05, 06:24 PM
Does it work properly on 60F?

Sounds like the mechanic did nothing and you deserve your $$ back.

On the 85 FSM:
Temp of air entering condenser: 90F
Compressor out pressure: 200-245 PSI
Accumulator pressure (low side): 26-35 psi
Temp out of the AC Air Discharge: 36-43F
Engine RPM: 2000
Read pressures just as compressor cycles off

Also, check this, is the sun sensor blocked or not reading right? If so, that wacks out the AC. Also check the proper operation of the outside temp sensor. These are critical inputs to the climate control.

chris85713
06-26-05, 08:53 PM
It seems to work the same with the temperature dial set on 70 as when it's on 60.....


and actually the mechanic did improve things a bit - before it was stuck on heat all the time, now it at least starts out on A/C. With the car parked in his air conditioned garage the system worked perfectly. This morning when I drove it to the grocery store it worked great all the way there (about three miles). It made it about half way home then started jumping between heat and A/C. That was aobut 8:30 with an outside temp of 85 to 90.

When I went back out at 11:30 with an outside temp in the very high 90's, it started on heat and stayed there.

The mechanic already asked for it to come back Monday morning to cure a different problem so I'm sure he'll keep going on the A/C.

N0DIH
06-26-05, 11:36 PM
Sorry, wrong post!