Thread: R134 conversion
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Old 04-01-2003, 08:02 PM
erubin erubin is offline
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Join Date: Mar 2003
Location: Los Angeles, CA
Posts: 445
R134 oil, evacuation, gauge measurements

Thank you for the suggestions/advise I received from you all. I'm sure R12 would be the better solution if I was looking for max cooling. We live in west LA. It rarely hits 90 and the humidity is not too bad. As such we don't usually need the chilling capacity many other parts of the country need. For this reason I will not go through the additional expense and/or inconvenience of converting to R12. As a DIYer I prefer sticking with R134 since I don't have to depend as much on using a shop. My logic may be flawed but I will stay with R134.

Since my compressor did not catastrophically fail and i'm sticking with R134 I hope to avoid flushing. I plan on removing the receiver/dryer, expansion valve and compressor. Then I will use compressed air to blow out as much of the oil as possible out of the lines, condensor and evaporator without removing them. This way I am starting with an almost dry-of-oil system and I can then put 4 oz of oil into the suction side of the new compressor, 2 oz into the evaporator and 2 oz into the receiver/dryer. This will provide the 8oz total called for my system. If the oil that is dumped out of the compressor contains no particles I will assume that a flush is not absolutelty necessary. I will then install my new (not rebuilt) Four Seasons R4 compressor, new expansion valve and at the last moment a new receiver/dryer. I understand every connection should have a new blue or green o-ring that has been dipped in the PAG or Ester oil. I will then try to find a shop that will evacuate and charge unless someone can recommend an economical vacuum pump to do the evacuation. I don't need a recovery system since the system is almost empty of refrigerant.

The compressor maker ships the unit without oil and recommends PAG or Ester oil for R134 applications. They would not advise one over the other. Does anyone know which would be my better choice? The out of business shop that did the R134 conversion with the previous owner did not put a tag on the car stating which oil was used.

Also I was wondering if I should invest in a small vacuum pump so that I could evacuate myself instead of trying to schedule an expensive visit at a shop. Any recommendations on an economical vacuum pump (don't need recovery since the sysyem is almost empty of refrigerant). When filling the system do you fill based purely on the weight called for or do you use gauges. I would like to know the gauge value for checking after loading and on going checks. I heard a rule of thumb is (2 x F) + 20 = high side pressure and 30psi for the low side. I know humidity should be factored in but would this be close enough? MB has 300D A/C pressure curves for R12 but not for R134.
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