Posted by 440roadrunner on May 06, 2009 at 09:41:26 from (98.145.76.31):
In Reply to: A/C help again posted by Jiles on May 06, 2009 at 08:26:16:
You PROBABLY have so many variable here that it defies imagination
First, is this an existing system THAT WORKED WELL?
Second, you are doing a refrigerant conversion. Think in terms of gas versus diesel. R134 is NOT R12
ARE YOU SURE, ABSOLUTELY SURE that you have enough fan past the condenser? (Might try a big 110V fan if you have one to move more air)
Anytime you make changes in a refer system (refrigerant change) , you can affect the whole system.
It's possible that the high side is too high because it is OVERCHARGED and the liquid is reducing the condenser capacity. An overcharge can fool you---there may be SOME OTHER CAUSE for the low side pressure that is making you think the charge is low, so you just kept adding refrigerant.
Plugged, undersized or WRONG expansion valve. You might check if you need to get a different TXV (if used) for R134 for your application YOU MAY simply have a Txv or other low side metering device going bad on you.
Correct on the sightglass. I don't even know why manufacturers install them. I'd charge slowly and watch the pressures and temp, and monitor compressor superheat. I'm not familiar with R134, but I used to use a rule of thumb of NOT LESS than 20*F compressor superheat. Be sure to check this with the sensor wrapped with insulation, as engine heat will affect your readings The LAST thing you want to do is slug the compressor with refrigerant
Air, water, or other "non condensibles" in this system can cause high side pressure, but WATER even very little can freeze up and plug up the metering device. I DOUBT that ice/ water is your problem--this usually comes and goes as an idle system will allow the plug in the metering device to melt over idle periods
Was this system "left open" for a period of time? Did you change (or does it have) a filter/ dryer?
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