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Old 02-07-2007, 08:16   #1
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AC unit pressures....

I have an old 11000 btu unit that burned a capacitor. I removed the unit and took it to a friends shop and he replaced the capacitor, performed the vacuum and re-charged with refrigerant R-22 to 60psi. Now the situation is that it will run for around 15 minutes and then the refrigerant pressure will slowly rise from 60 psi to 70psi and the compressor shuts down as soon as the pressure goes above 70. I bypassed the high and low pressure switches and also the thermostat but still the unit shuts down as the pressure rises. Is R-22 the correct refrigerant?, Could it be that it has too much refrigerant? Is 60 psi the correct pressure? By the way this happens with the unit in the boat and also in the shop with a fresh water supply. We even cleaned the condenser with drano. .....


Help...it is way to hot here in the caribbean....
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Old 02-07-2007, 09:47   #2
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It is really tough to tell the proper charge for an a/c system, unless the weight of the charge is labeled on the unit & you weigh the charge you put in. I'm guessing the labels are unreadable? R-22 is probably the right refrigerant, but again, without the label... The problem you are experiencing sounds like too much superheat. The refrigerant flashes to a vapor, then continues to be heated, raising you low side pressure. This is commonly caused by low refrigerant level. To get a full picture of what is happening, you really need to measure pressure on both high and low sides while monitoring evaporator temperature. What is the temperature of the evaporator inlet vs discharge? Overfilling will make the discharge feel really cold. Underfilling, not cool enough. Bypassing the switches is a recipe for a blown compressor. You could try adding refrigerant, but this too could seize your compressor if not done properly. Sounds like you have run out of expertise and are left with guesswork. Unless you are willing to risk seizing your compressor, call in a local expert.

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Old 02-07-2007, 15:54   #3
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There really was a plate installed on that system when it was new, specifying the correct gas and pressure. R22 was the norm for fixed installations (homes) but not necessarily for mobile ones. If you have a sealed compressor, it could well be R22 but in recent years there have been a LOT of gas choices. Offhand I'm not sure of the pressure, I'm on the road and no references to check but you can probably find typical R22 pressures on the web. Too much pressure can cause a system to freeze up--and then build overpressure. Moisture in the system can also freeze up and block it that way, there may be a "receiver/drier" cannister in the system and that eventually wears out as it absorbs moisture. (There's one in moible systems, but a fixed system might just rely on being dried before sealed.) Conservative approach is to replace it every time the system is opened for work, to be sure, if there is one.

I'd start by looking for the rating plate on the unit, which should tell you the right gas. Assuming the friend was chosen because he's in the AC business <G> what were his thoughts on it?

As Brett mentions, the correct way to check an AC system is by running dual pressure gauges while it is operating--that will tell you what the system is doing more precisely. They're usually sold for about $45 at auto shops or online (get a set with matching fittings, IIRC R12/R22 both use "schraeder" type fittings, the new R134a, etc. gasses DO NOT) and fairly simple to use. Or ask your friend to come over for dinner--and bring his R22 gauge set.<G>
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Old 03-07-2007, 05:05   #4
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The system has been over charged the low pressure side should be 50-52 psi when charging with r22 refrigerant.Did the filter/dryer get changed should be changed on every system that is opened.Greg
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Old 03-07-2007, 06:15   #5
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Ok...
What I have is a Copeland compressor. It does use R22 refrigerant. It is thermally protected. Model #JRF4-0075PAA. After re-cleaning the condenser, removed some refrigerant to lower the operating pressure to less than 50 the unit still shuts down after 15 minutes or so. It just goes "click" and the compressor shuts down for a while. Then it starts again for another 10 minutes or so and down and so on.....All of this even bypassing the external pressure switches and thermostat. It seems to be internal protection that trips the compressor. Could it be a bad compressor? What confuses me is that when it cools it cools really well.
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Old 03-07-2007, 07:18   #6
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This sounds like a query for Richard Kollmann, author of “12 & 24-volt Refrigeration Manual” and “Do-It-Yourself Boat Refrigeration”, and a very knowledgeable & helpful expert.
KollmannMarine Boat Refrigeration Specialist

Post your questions on his Technical Foruum, and receive an answer from Mr. Kollmann within a short time:
kollmann-marine.com :: Index
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Old 03-07-2007, 08:11   #7
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Copeland Compressors- Electric Company- Hvac Plus -
Claims they service and sell Copeland compressors, a division of Emerson for 20 years now.
I'd guess the "click" is an internal thermal breaker shutting the compressor down due to something overheating. Time to ask Kollman or Copeland what is in that unit and why it would be failsafing that way.
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Old 03-07-2007, 12:46   #8
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More info...

Ok ...

Found out the unit has a 3/4hp compressor. It is 8000 btu not 11k. What is clicking is the overload motor protector. It is an external little thermal switch that opens as certain temperature is reached. I lowered the pressure to zero at the R22 reading of the dial. It then goes up to around 10 psi. Still the compressor feels really hot to the hands. Currently testing to find out if it trips again.
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Old 03-07-2007, 13:28   #9
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Well, it tripped again.....the compressor gets way to hot and trips the thermal switch. Even though the pressure stays belo 10 on the R22 dial. I guess this is one of those things that someone else will have to do. I quit.
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Old 03-07-2007, 13:49   #10
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Refrigeration systems are simple. You know, like "poker, a simple game".<G>

It's very possible that it is tripping out because the system is overheating--because your friend added R22, but didn't check the oil charge. There's also got to be a specific amount of oil in each system, without it the compressor would overheat and trip out. Or burn up.
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Old 03-07-2007, 13:55   #11
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Its a sealed compressor. How do you check the oil?
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Old 03-07-2007, 14:01   #12
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Well...when you are recharging a system one way is to physically pour out the old oil, and then simply add a new correct oil charge. Oil's cheap enough to just "use new" and not worry about contaminants in the old stuff. Since the oil vaporizes and moves through the system along with the "freon", if there's been a freon leak there may have been an oil leak from the same release point.

Or, it could just be there's something worn out in the compressor, a bearing seizing from contamination, coils that have swollen up...all the usual ways "motors" can fail.
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Old 04-07-2007, 09:04   #13
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How long was the unit on vacuum? Did you draw a full 29.9"? Start by putting the unit on vacuum for a couple of hours at least. This will ensure no water remains. Some oil will be drawn out. Does the oil smell burnt? This would signal a burnt compressor. Find out what the approproate refrigerant charge is, and weigh the R-22 you put in. Preferably use new refrigerant. Likewise, try to find out what the oil charge is supposed to be and add about 2/3 that number. Sould be a couple of tablespoons.

I suspect you were under charged. You still haven't said what the evaporator inlet and outlet temps were doing.

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Old 05-07-2007, 05:31   #14
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The system has a blockage most likely either a blocked capilary or tx valve which ever is used in the system,or blocked filter/dryer was this change.Greg
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Old 05-07-2007, 09:17   #15
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Blockages cause lower low side pressure, not higher.
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