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Cadillac compressors did not cycle until about 1980. On the 60's era cars, when you moved the temperature lever toward warmer, you'd hear some kind of "hiss" as the air temp changed. Climate control did not have the compressor cycle, either. I still have a '74 Cadillac with working Climate Control (in my family for years) and the compressor is always on, if the CC is on. This was true from '64 up, we had several of these cars and they never iced up, either. Was this bypass in use that long?

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Kind of depends. Some could handle it but most of the compressors and clutches of that era were not designed for the continual on/off operation the temp control would require. When the engine is moving at a fairly high RPM it is a huge shock to start and stop the mass of the larger reciprocating piston affairs common at the time. A one time on and then maybe an off at the end of a trip or at least a few miles down the road wouldn't be too hard. An on and off every minute or two is another story.

If you do find a suitable compressor with a clutch, if it needs a go thru, finding compressor parts for some units of that era is another exercise in patience. The 12v Lehigh that Packard and several aftermarkets used is a perfect example. I can imagine less commonly used compressors are even worse.

hi howard; i have been following your ac efforts and your quest for the 6 volt clutch. fred mauck is a long time pi member that has a 53 i believe that he added air to, he has one of the under dash units and runs the 12 volt clutch on 6 volts and it seams to work fine the last time i saw the car. he is a great guy and i am sure he would be happy to talk to you owens king auto. i will pm his number if you want to give him a call.

I know there are several Sandens running on 6v cars. Fred is now another confirmed.

What I believe is happening is because the generator output is at it's normal around 7.4v, the clutch is able to pull in because of the higher charging voltage. Sanden specs say minimum pull in is 7.5v so there is probably a bit of a fudge factor. I know mine won't pull in on a straight 6.3v and I believe Jim McDermaid in AZ tested his with the same results.

Appreciate the offer of the phone # and maybe will take you up on it at some point. For now I'm going to try out that small extra battery/relay module I made -- at least as a start. If it doesn't work out, then it's a simple matter to change a couple of wires and go with 6v. What I am hoping to do is come up with something proven that can work for those that won't take a chance on the Sanden running directly on 6v so they could still use the compressor.

Am curious if Fred changed his blower motor though. I made some tests and felt the 12v motor would work adequately on 6v. I wanted to document the difference so did change it to a 6v universal motor. What I found is the 6v motor puts out about a third more air than the 12v running on 6v but not nearly as much as the 12v running on 12v.

We have blogged about this several threads ago.

As my 54 Cavalier has a separate 12 volt system (alternator and battery) to run the Add-on A/C.

I have done some research:

First, a compressor clutch on a Sanden draws 3 or 4 Amps at 12 volts. Nobody makes a 6 volt clutch and the original compressors ran continuous unless you took the belts off for the winter. The clutch won't engage much below 7 volts, and not at all on 6 volts.

The other big power suck is the blower for the A/C Evap unit inside the cockpit which as I recall was drawing about 15 Amps on high speed.

My 12 volt system can't keep up on a good summer day in Phoenix AZ.

My solution is to see if the blower can spin the proper direction and run fast enough on the 6 volt system. (I realize I won't get high speed). If the blower motor is permanent magnet type I will have to flip it end to end and change the squirrel cage back. I rarely run the blower faster than low speed which cools just fine especially with R-12.

Haven't had time to pursue this yet.

I could then keep the existing 12 volt system which will have no problem running the clutch. Or buy one of those 6 to 12 volt converters for just the clutch.

The A/C system draws way too much power to try and run it on a 6 to 12 volt converter as the 6 volt system is good for about 45 Amps from the generator and the load from the converter calculates to about 45 Amps.

My 12 volt system is totally separate from the cars original 6 volt system. I use an Optima 6 volt battery which leaves plenty of space on the battery shelf for an RV type 12 volt sealed Glass Mat battery. The Optima's are sealed also so no corrosion.

The 12 volt is handy for using my engine analyzer and timing light. And I am looking for an FM to AM radio converter as all the AM's in Phoenix have gone hate talk.

Jim

I don't know where this electric bypass solenoid stuff came from.

On the original Packard system the only compressor control was to take the belt off.

When the heat load in the system falls the pressure in the system also falls. There was a high pressure relief valve and that was it. In cold weather the TXV will close and the low side run a vacuum while the high side condenses into liquid. You can't compress a vacuum so not much happens.

So for a car in Texas there is no reason to screw around with batteries in the trunk, and cables, and all that non-sense unless you want to dazzle everybody at a CCCA cocktail party.

I can see Jim hooting that up in my mind right now. It must have been hilarious.

I don't know where this electric bypass solenoid stuff came from.

Right out of the 53-54 service manual. We're talking postwar system operation in the thread and what can be obtained in the way of off the shelf components today if someone wants to add AC to their car.

The prewar unit control was just an expansion valve -- the whole AC was essentially a small commercial freezer design and fairly basic but still compact and advanced for the day. Probably be just as hard today to find a quality commercial valve that could match the output to work with the the auto evaporators available. Auto TXV's today are really basic -- if it's even a valve and not just a CCOT system.

The Packards of the 6 volt erra used no clutch at all. The on and off cycle for air was a bypass solenoid valve for the freon. This site has a complete excerpt on the installation and charging of the system.