r12 refrigerator pressures

[thecarpenter]

Hey guys , new here, usually in residential tech area.... I have an older refrigerator that is not cooling. Why are there 3 tubes coming off the compressor, 2 to the condensor and the third to the evaporator. I put a line tap to check the pressures but don't know what the low side should be. What should the equalized pressure be at ambient 70 F?
THanks
Greg

[welling service]

unknown. Depends on how much R12 is in the system. Is the comp running?

[kamersoutdoor]

One of the two into condenser isn't a process stub?
Maybe looks as if going to condenser?
Just a thought!
Pull charge and weigh in with adequate replacement!


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[kamersoutdoor]

unknown. Depends on how much R12 is in the system. Is the comp running?

Yeah, start here first!

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[icemeister]

Look at your PT chart for R12. It holds the answers to your questions.

The pressure at 70ºF should be obvious.

Then think about how a typical domestic refrigerator works and what temperature the evaporator must be to achieve 0ºF to keep your ice cream frozen.

[thecarpenter]

compressor is running, was wondering what design low pressure should be, can see a fourth tube that is stubbed off, sorry, not thinking cause I do have a pressure chart so.... 0 degrees for freezer looks like around 9 PSI for evaporator, ambient 70 degrees around 70 PSI. No cool evaporator line on compressor so I can't see any other problem other than low charge, fans working, when I finally got tap in place, about 50 PSI and pulled down to 0 PSI when running.
Thanks for your help

[jackal]

I did appliance repair a long, long time ago and if memory serves you could be looking at an oil cooler. Seems the compressor oil cooling was a small circuit routed through the static condenser, but it should have a return line into the compressor. Look again, are you sure there isn't another tube?
As far as suction side pressures listen to icemeisters advice, but seems self defrost models, R-12 would typically run around 3 lbs and manual defrost types would be a little higher, like 6 or 7 lbs.

[icemeister]

compressor is running, was wondering what design low pressure should be, can see a fourth tube that is stubbed off, sorry, not thinking cause I do have a pressure chart so.... 0 degrees for freezer looks like around 9 PSI for evaporator, ambient 70 degrees around 70 PSI. No cool evaporator line on compressor so I can't see any other problem other than low charge, fans working, when I finally got tap in place, about 50 PSI and pulled down to 0 PSI when running.
Thanks for your help

You're close, but missed my point about thinking of how a refrigeration system actually works. With a 0ºF evaporator there wouldn't be any heat transfer from a 0ºF freezer. The evap has to be colder than the freezer.

[MicahWes]

You're close, but missed my point about thinking of how a refrigeration system actually works. With a 0ºF evaporator there wouldn't be any heat transfer from a 0ºF freezer. The evap has to be colder than the freezer.

Also, the condenser should't be at a pressure equivalent to condenser ambient.