1977 Cadillac DeVille

¯\_(ツ)_/¯ said:

I have been driving this all over the place and getting a consistent 13 mpg, which seems pretty good for a 7 liter engine moving an entire living room around.

Today I hooked up the gauges hoping for even the slightest bit of pressure in the air conditioning system:

Started the engine, opened the valves and...

Womp womp.  At some point I'll hook up the vacuum pump and see if I can find a leak; today I had to tear the dash out of our truck to fix its' air conditioning- one GM HVAC nightmare at a time.

You can also pressurize it with nitrogen if you have access to a bottle and regulator.  If you have any friends that do HVAC service a trace of refrigerant along with the nitrogen and an electronic leak detector are a big help. 

I will note that both my Raider and Porsche had zero pressure on the air conditioning systems when I got them, and both had shot compressors. I replace the compressors on both and charged them up and both of them have held the charge for multiple years now and blow cold. So you may not necessarily have a notable leak in the system It just maybe has been sitting for a long time and slowly lost it over years. Should be easy enough to tell once you do the vacuum test though.

I will add a little more diagnostic. If it apears to hold vacuum for a few minutes, reach in and wiggle/turn the compressor a little while you watch the gauges. If the vacuum leaks the compressor seal is bad.

Don't try and tell me that our shop doesn't see some variety:

Hooked up the sad little vacuum pump, pulled as much vacuum as it could manage, and closed the valves.  Did other stuff for an hour, came back and spun the compressor, wiggled lines, poked stuff, and:

Gonna go walk the dogs and check again but this seems promising.  What's the favored R12 replacement these days?

It was still holding vacuum with the same gauge reading when I got home, neat.

I have an unopened can of R12 that came with the house. Not sure if one can is enough for that system though, but you'd be welcome to have it

In reply to ¯\_(ツ)_/¯ :

I have been using iso butane for many years now. Runs at slightly lower pressure than R12 and cools a little better, also compatible with any lubricant, and it is a biggish molecule. Far better than running R134.

I've just been using R134a in all my old cars. The A/C in all of them blows cold (colder than my GTI, incidentally). 

In reply to TurnerX19 :

More details please - any changes that need to be made to an r12 or r134 system to use iso butane? Where do you get it from?

In reply to Racingsnake :

No changes at all to install into R12 system. An R134 system that uses an orifice tube will need to be back dated to an R12 tube. I have bought from Envirosafe. It has been quite a long time, and I still have quite a bit in stock, as I am only maintaining one system anymore.

Bill came by, my terrible cheap AC gauge set did its' best to sabotage him, and now the Cadillac has fresh smelly refrigerant in it:

The compressor sounds bad but the air blows cold!

I regret that we had to stop talking car stuff so that I could attend the very important meeting that I'm typing this post during.

Drove it for about 45min- the compressor quieted down a bit and the air certainly blows nice and cold going down the road with some wind helping the crusty blower motor push it through the vents.  We'll see how long this compressor lasts!

I somehow missed all this gorgeousness and gorgeosity. I like.

In reply to TurnerX19 :

Thanks, sounds like a good option.

For a second there I got excited about the Volvo wagon parked out front until I realized it wasn't yours :)

Ice cream pickup and down to the parents house for father's day, we parked next to something that made the Cadillac look new at the ice cream place:

The air conditioning continues to work but has a max speed of about 75mph or the belt slips- the car also feels way, way more "correct" with the windows down.

Do these cars have the thing where over a certain throttle opening amount they shut off the compressor? I know a lot of '80s GMs have that. Of course by 1977 opportunities to drive 75mph were much fewer and far between especially east of the Mississippi.

GCrites80s said:

Do these cars have the thing where over a certain throttle opening amount they shut off the compressor? I know a lot of '80s GMs have that. Of course by 1977 opportunities to drive 75mph were much fewer and far between especially east of the Mississippi.

I was thinking the same thing

Alternator cooked itself- replaced with an Advance cheapie and it seems fine.  The blower motor seems to have done... something.  It runs continuously when the car is off now, so it's unplugged for the moment until I feel like figuring it out.

The car did also achieve a new high score of 14mpg on an all-highway tank.

¯\_(ツ)_/¯ said:

Alternator cooked itself- replaced with an Advance cheapie and it seems fine.  The blower motor seems to have done... something.  It runs continuously when the car is off now, so it's unplugged for the moment until I feel like figuring it out.

The car did also achieve a new high score of 14mpg on an all-highway tank.

Well, at least there's something out there that gets crappier highway mileage than (either of) my Sequoias.....

Then again, that thing probably weighs damn near as much. 

I'm a bit surprised though....I figured those big old caddies, once you got them up to speed, would just get like 30mpg simply using mass and momentum. 

¯\_(ツ)_/¯ said:

The blower motor seems to have done... something.  It runs continuously when the car is off now, so it's unplugged for the moment until I feel like figuring it out.

Blower motor speed resistor either melted to itself or shorted by debris/mouse nest/squirrel testes?

newrider3 said:

 

Blower motor speed resistor either melted to itself or shorted by debris/mouse nest/squirrel testes?

Blower motor resistor shouldn't be seeing power with the car off, right? 

Seems like time for some studying of the wiring diagram.

irish44j (Forum Supporter) said:

I'm a bit surprised though....I figured those big old caddies, once you got them up to speed, would just get like 30mpg simply using mass and momentum. 

I think they would if there wasn't 7 liters of engine and a massive old 3 speed auto to spin.  I bet if you put one on a trailer and just kept the rpms up it would get the same fuel economy as it does when actually driving.

In reply to pres and newrider:

Seems like something may be funky in the HVAC controls themselves- switching back and forth, I get a "generator" light on the dash when on some settings and the surprise blower motor on others, all with the car off.

For now, windows down.

Things were getting strangely grumbly at low speed, which eventually I narrowed down to rear axle bearings.

This thing has the biggest pinion gear I've ever seen, I guess because the axle ratio is like 2:1

C-clips are a bit worn but not alarming so I reused them.

Obligatory "you can see through the axle" shot:

And back together with some fresh Timken bearings and driving.  I should probably do the same on the front hubs in case those bearings are equally ancient.