Quote:
Originally Posted by tyl604
Diseasel300 - wow; you are really a fount of information. Have never seen that explanation about R12 vs 134a. Now I understand a bit more.
Thanks for that.
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The heat capacity of the 2 gasses is different as a result of their molecular composition. The R134a needs to run at an elevated pressure compared to R12 and reject more heat to do the same amount of work in the same system. If everything is perfect and all the planets are aligned, the gas in the condenser will just be leaving the final loop as a liquid. In the real world, the last loop or two in the condenser will be liquid depending on ambient conditions.
If the charge is low, or the wrong metering device is installed, the head pressure does not build adequately to condense the gas to a liquid. That is where you get the flashing sight glass and poor cooling performance, the expansion valve is open too far to allow head pressure to build sufficiently to condense the gas due to a low volumetric charge. On a very hot day with high humidity, these systems will run a 250-275PSI head pressure vs 200-225PSi on R12.
Converse to popular opinion, you need the pressure and you need the heat in the system to do work. The people who stack 2 parallel flow condensers on top of each other are defeating the purpose of the the condenser. The first one condenses the gas, the 2nd one is acting as a liquid receiver, the result being a gross overcharging of the system and very poor cooling performance in cooler or temperate weather. W123 and Gen I W126 cars need an updated condenser to run R134a, they were barely adequate to run R12. The Gen II's are a different story, no upgrade required. The stock system will handle it just fine with a replacement expansion valve and the correct oil.