Packard Forum Index » Post-War (1946-54)

If you're mechanically inclined enough you can do like the original Packard a/c and make the clutch solid so it's always running, just take the belt off when it cools off enough not to use it. A welder comes in handy sometimes.

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This is pretty much the way things have been since at least the early 90's and maybe even earlier. Lower end aftermarket systems used the clutch as soon as compressors became available with robust more heavy duty units but factory system cars up until the change did the constant on-reheat the cold air-style temp control. IMHO, that is a superior system as there is no humidity change as happens when the clutch drops out and suddenly thawing moist air is blasted into the car.

Mostly because of fuel economy numbers and trying to squeeze the last drop for the fleet averages, most US companies almost overnight adopted the cycling clutch. I am sure cost of components had something to do with it as well since the clutch system is much simpler with no POA or assorted similar temp control valves and plumbing to worry about.

HH and ATMWOO, thanks for the explanation. My ignorance bucket is less full now. Appreciate it.

(o{I}o)

Thank you for the info on the oil type. I didn't know that, I had always used compressed PAG, I do replace the drier anytime the system is open or vulnerable but I hadn't ever put any thought into why.

I also didn't know about the constant on style, that blew my mind. Now the next car show I go to I'll be looking for ac clutches. I just seems odd that such a power drain would be the norm.

But then nobody knew sliced bread would be such a hit till somebody tried it !

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Most compressors had a clutch after about 54-55 but most of those were designed to turn on once when the AC was turned on and off when AC was turned off--not the constant on several seconds and then off cycle modern systems do to keep the temp in a narrow range. Compressors were large with a lot of internal mass to get moving quickly and constant on/off put a tremendous strain on just about everything connected. Mid-late 50's saw the more robust clutches and better and lighter compressor internal designs hit the market. Aftermarket units took advantage of those and the cycling clutch because there was much less to go wrong with simpler pieces and less expensive to have to plumb or design for different applications.

Temp control on most pre 90's higher end or integrated factory units was actually done by several methods in the refrigerant circuit. Early on Packard (and several others) used hot gas bypass where hot refrigerant gas was introduced directly into the evaporator just after the expansion valve to bring the temp up. 53-54 Packard (which had no clutch) was done electrically via a thermostatically controlled solenoid valve and 55-6 with a clutch used to turn compressor on was done mechanically via fixed temp modulator valve. Other manufacturers higher end systems used other methods to either starve the evaporator of refrigerant so it wouldn't get below a certain temp or keep internal evaporator pressure up for the same result.

All of these systems had a fixed temp for evaporator a few degrees above the point where moisture would freeze. In order to provide a comfortable delivery temp, some would vary fan speed, some would blow the cold air through a temp controlled heater core to re-warm, some had a mixture of hot and cold air blended in a mixing plenum before delivery and some a combination of all. Some independents and even a big 3 mfg on a model or two did use custom aftermarket type systems but they were styled appropriately so "factory" but used the cycling clutch.

Those with the compressor and evaporator constantly on and always de-humidifying were, IMHO, a more comfortable system. Alas, also more expensive to build plus you took a hit on horsepower and fuel efficiency.