Re: air conditioning 49 or 50 Packards

Posted by HH56 On 2010/9/10 15:59:59

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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.

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As to the R12 to R134 change, I'm glad you have had success but there is a big issue with oil compatibility. 12 uses a mineral base and 134 uses PAG or Poly Alkaline Glycol. The two are not compatible at all and mixing will destroy the effectiveness of both as well as prevent microscopic droplets being carried through the system to lubricate other items. Since the oil does pool in various areas, it is almost impossible to get it with vacuum alone. Usually a drain of the compressor and a system flush is needed as well.

134 also has different pressure and temp curves. While most modern systems are over-engineered and won't be too adversely affected, those with marginal condenser or evaporator capacity will be. Straight 134 is not as efficient as 12 so at equivalent pressures is about 10 degrees warmer but there are some approved products that can be mixed in to bring to almost the same level.