glaird
27-07-2010, 05:54 PM
Hello,
I have a 1500 BTU freezer in an Ice Cream Vending Machine that I am repairing. The unit was originally an R12 unit that I have converted to MP66. It was not working when I started the repair work and I have no idea what the correct R12 high side and low side pressures were. The unit label states that the charge should be 15 Oz of R12. I have taken 80% of this value (MP66 adjustment) leaving a 12 Oz MP66 charge. I have added a larger liquid line filter so I have then added 1 more oz to account for this--the total charge is about 13 oz.
I have had a number of problems with the unit, most of which have been fixed now. The last being a restricted cap tube. I cut off the first 2" of the cap tube and this fixed the restriction. My high side pressure is running about 125 PSI, the low side about 0 PSI. The compressor is running about 6 amps, the RLA value. I may be a little low on charge--I haven't added more for the reason below.
When I operate the freezer and the freezer cabinet is close to its set temperature (1 degree F) my suction line temperature seems to oscillate with a pretty high amplitude. I have attached a pdf file with a chart of the oscillation. I am thinking that if I add more refrigerant, the oscillations will get larger and I may return liquid back to the compressor--so I am hesitant to do this.
I have taped the cap tube to the suction line for most of the suction line length (50"). The suction line and the cap tube are inside an insulated sleeve. I did this with the idea of precooling the refrigerant before it hits the evaporator. I am wondering if this thermal connection may be causing my oscillation.
Has anyone seen this sort of thing before?
Thanks,
Greg Laird
I have a 1500 BTU freezer in an Ice Cream Vending Machine that I am repairing. The unit was originally an R12 unit that I have converted to MP66. It was not working when I started the repair work and I have no idea what the correct R12 high side and low side pressures were. The unit label states that the charge should be 15 Oz of R12. I have taken 80% of this value (MP66 adjustment) leaving a 12 Oz MP66 charge. I have added a larger liquid line filter so I have then added 1 more oz to account for this--the total charge is about 13 oz.
I have had a number of problems with the unit, most of which have been fixed now. The last being a restricted cap tube. I cut off the first 2" of the cap tube and this fixed the restriction. My high side pressure is running about 125 PSI, the low side about 0 PSI. The compressor is running about 6 amps, the RLA value. I may be a little low on charge--I haven't added more for the reason below.
When I operate the freezer and the freezer cabinet is close to its set temperature (1 degree F) my suction line temperature seems to oscillate with a pretty high amplitude. I have attached a pdf file with a chart of the oscillation. I am thinking that if I add more refrigerant, the oscillations will get larger and I may return liquid back to the compressor--so I am hesitant to do this.
I have taped the cap tube to the suction line for most of the suction line length (50"). The suction line and the cap tube are inside an insulated sleeve. I did this with the idea of precooling the refrigerant before it hits the evaporator. I am wondering if this thermal connection may be causing my oscillation.
Has anyone seen this sort of thing before?
Thanks,
Greg Laird