Standard engine-drive Refrigeration issue - Low pressure side...

[MoonlightSailor]

Aloha!

I have a standard engine-drive refrigeration system with york type compressor.

Fired up the refrigeration system that was working the last time I ran it. Now its not working/cooling. Low pressure switch is turning off compressor. Here goes...

Initially ran it…opened the high side on the compressor and then slowly opened the suction side of the compressor to prevent slugging back at the compressor. The compressor ran for a while and then turned off and wouldn’t turn back on. The ice box didn't frost anywhere or at the expansion valve.

So then I connected the pressure gauges and initially got readings of 54 on low side and 90 on high side.

Then turned on compressor and and opened the valves again in the same order on the compressor. The low side dips below 0 and the the compressor turns off at -10. The compressor turns back on once it reaches 10 psi, then turns off very quickly when it is drawn below -10.

Sounds like a leak or low on R12. But the low pressure reads 40-50 when system is at rest. I don't think there is a leak. What do you think? System was running fine before. I’m sure you’ll have questions.

Matt

[Richard Kollmann]

Originally Posted by MoonlightSailor

Aloha!

I have a standard engine-drive refrigeration system with york type compressor.

Fired up the refrigeration system that was working the last time I ran it. Now its not working/cooling. Low pressure switch is turning off compressor. Here goes...

Initially ran it…opened the high side on the compressor and then slowly opened the suction side of the compressor to prevent slugging back at the compressor. The compressor ran for a while and then turned off and wouldn’t turn back on. The ice box didn't frost anywhere or at the expansion valve.

So then I connected the pressure gauges and initially got readings of 54 on low side and 90 on high side.

Then turned on compressor and and opened the valves again in the same order on the compressor. The low side dips below 0 and the the compressor turns off at -10. The compressor turns back on once it reaches 10 psi, then turns off very quickly when it is drawn below -10.

Sounds like a leak or low on R12. But the low pressure reads 40-50 when system is at rest. I don't think there is a leak. What do you think? System was running fine before. I’m sure you’ll have questions.

Matt

I do not understand why you are opening and closing compressor valves risking explosive damage. Your engine drive system will have a low and high pressure switch set to stop compressor from operating below a vacuum of 10 inches and above a safe operating high pressure. When nearing a vacuum of 10 inches the evaporator holding plates are solidly frozen. The expansion valve on that system requires a refrigerant storage receiver tank. Unless there is some liquid refrigerant stored in this tank it would indicate low on refrigerant pressure on a warm day at 40 to 50 psi vapor only. Also the refrigerant liquid flow sight glass when compressor is first energized will go from clear to solid color or bubbling refrigerant, if not add refrigerant.

These system that experience liquid slugging failures are do to excessive compressor speed on clutch engagement or an oversized expansion valve. Many designs use a method of suction line accumulators to slowly meter liquid return.

[sfnz]

how long since you last ran it prior to this startup ?, try running your finger below the shaft and see if you pick up oil.... if so chances are a shaft seal leak, all open drive compressors suffer from this if left long enough

[Richard Kollmann]

All AC automobile compressors now used on engine driven pleasure boat refrigeration require occasional rotation for shaft seal to retain oil. The York compressor was one of the first generations of auto compressors and used a rubber V seal and relied on the pulley clutch bearing to keep shaft sealed centered. The next generation of AC compressors all use a carbon spring loaded seal and a floating drive shaft.

sfnc is correct that systems out of service any length of time can lose refrigerant through a dry seal. If the York clutch pulley bearing has lost its lubricant any wear will cause refrigerant loss, if so in addition to presents of oil on compressor face there will be traces of red metal colored oxide if clutch bearing needs to be replaced.

The normal corrective action for shaft seal leakage is add refrigerant as loss of oil from shaft seal is very small. Your compressor contains 12 to 13 ounces of oil so unless there is a lot of oil every where do not add oil.