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Old 27-12-2017, 12:58   #1
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Refrigeration system possibly overcharged...???

Greetings,

History of situation:
Tarawa - System developed a leak at the small copper tubing that connects to the high/low pressure switch. That was fixed and we recharged the system. I can't remember exactly how much R12 we put in the system but it was close to what we left San Diego with.

We returned to Hawaii and stopped using the system.

Upon trying to use the system to go on an interisland cruise, I found that the compressor (belt driven from a 3HP electric motor) seemed to be bogged down and the clutch on the compressor was slipping. I thought the clutch was bad but that was not the case because I switched clutches.

The compressor obviously seems like it has too much of a load on startup.

However, I am albe to engage the clutch and it will spin a few revolutions before the clutch starts to slip. I found that if I engage the clutch for a few revolutions and then turn it off when it starts to slip and repeat this process, I'm eventually able to keep the compressor running without slipping.

I'm suspicious that it is over charged. Suggestions are appreciated.
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Old 27-12-2017, 13:12   #2
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Re: Refrigeration system possibly overcharged...???

Too much of something - but what?

Water vapor
Oil
Good old fashioned air
Or refrigerant

Which would include the right amount of oil but too much of it in the wrong places.

Questions to consider:

- Do you have a sight gauge? If so did you use it to determine how much refrigerant to add?
- Do you have a fixed orifice or an expansion valve (TEV)?
- Do you have service ports and gauges? If so, what pressures do you see?
- Was the system evacuated before fill? If not, was the refrigerant pressure low enough for contamination to be a concern?
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Old 27-12-2017, 14:17   #3
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Re: Refrigeration system possibly overcharged...???

Thanks for your quick reply and valid questions.

Yes, I have a sight glass (see pic).

Yes, I used a gravity scale to measure the amount I put in the system.

I have service ports and guages....don't currently know what the pressures are.

Yes, I put the system on vacuum pump for around 2-4 hours before recharging. I am aware that ideally the vacuum should be on for longer periods.

FYI - I have Nigel's book on refrigeration for pleasure boats.
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Old 27-12-2017, 14:22   #4
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Re: Refrigeration system possibly overcharged...???

Misunderstood how to upload pic from last post...Here is the sight glass.
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Old 27-12-2017, 15:51   #5
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Re: Refrigeration system possibly overcharged...???

The gauge set Without needing any more or losing any refrigerant can be used to test pressure and compressor.
Connect Red and Blue hose.
Open blue gauge valve then quickly close it to purge air from blue hose.
Repeat air purge on Red hose.
Using one of the 1/4 in flare refrigerant caps place it on center gauge port that is intended for a yellow hose.

Now open red valve on gauge set all the way.
open blue valve a 1/2 turn and power up compressor.
Compressor should run and now slowly restrict refrigerant flow by almost closing Blue valve If this is an air cooled system the high pressure should be less than 150 psi.
If water cooled high pressure should be less than 130 psi.

Low pressure can now be adjusted by regulating blue valve from 10 to 15 psi. With system running stable try closing blue while watching Blue valve do not allow high pressure to exceed max pressures above.

Describe the line repair to pressure switches. Was this line soldered at the high pressure line T ?
Are you sure the pack-less valve in picture is open full counterclockwise?

I would need to know a lot more about the type system you have before offering more help.
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Old 27-12-2017, 15:52   #6
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Re: Refrigeration system possibly overcharged...???

Compressor not running:
Low side pressure is 77
High side pressure is 80
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Old 27-12-2017, 16:12   #7
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Re: Refrigeration system possibly overcharged...???

Three psi difference in gauges is not a problem. Your 3 HP motor can start compressor too fast if system has too much refrigerant. If the gauges are connected right now what happens to gauge reading when motor is energized for a couple seconds.
Where in the system is the red hose connected? Is there a valve on refrigerant receiver (king valve) ?
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Old 27-12-2017, 16:19   #8
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Re: Refrigeration system possibly overcharged...???

Yellow hose is on guage connected to itself on back of guage.

Red guage hose is connected to high side of compressor and rotolock valve is cracked open a bit from the back seated position.

BTW...I have your book...we are coming full circle again.

I have not started the compressor yet. I was confused by what you said to do with the yellow hose from the guages.

I feel we can trouble shoot this easier if you give me a call depending on if you are free or not. I will compensate you for yor time.

808-223-5047
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Old 27-12-2017, 17:32   #9
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Re: Refrigeration system possibly overcharged...???

Update:

The system has an expansion valve at the plate. Also has a receiver. It is water cooled.

Initial compressor pressure readings are in photo. I was able to close low pressure valve on gauges without a fuss.

I can hear gas rushing past the expansion valve when I put my ear to it.

The red hose is connected to the high side of the compressor.
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Old 27-12-2017, 17:35   #10
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Re: Refrigeration system possibly overcharged...???

Pressures are dropping. I've had it running a little over an hour now.

Low pressure: 5
High pressure: 100
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Old 27-12-2017, 17:38   #11
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Re: Refrigeration system possibly overcharged...???

Any idea what is causing the "chirping" noise at the clutch unit? See attached video.

Update: the chirping sound slowly went away. Took about an hour or so.
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Old 27-12-2017, 18:10   #12
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Re: Refrigeration system possibly overcharged...???

I just sent you some $$$ for the book and your extra help! Mahalo! (as we say in Hawaii)!
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Old 27-12-2017, 18:40   #13
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Re: Refrigeration system possibly overcharged...???

Sight glass video attached
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Old 27-12-2017, 21:04   #14
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Re: Refrigeration system possibly overcharged...???

I quit using the phone years ago mainly because I do not think fast enough with my answers. I have never charged for my services so I won't start now.

The gauge pressures at first show low at 20 psi and high at 115 psi. How many minutes into the run was this picture taken?

After one hour low pressure gauge shows 5 psi and high pressure 100 psi.
Picture of sight glass is mounted vertical and is either full or empty?

The sight glass if full of refrigerant would indicate enough refrigerant.
Low pressures in both cases appear to be in the ball park.
High pressures are usually not this low unless seawater is cold or refrigerant charge is low.

Refrigerant pressures and sight glass can confirm performance. But the original problem of overloading the clutch and belt system is the real problem. At this point the problem does not seem to be refrigerant volume or refrigerant flow restrictions. Can you explain why the over load condition went away during these test runs? What might you have done that could relieved the start and run overload?

Question there is a large bearing inside compressor clutch, Look behind clutch for signs of red oxide dust that would indicate a problem there.

Its is midnight now, time for bed.
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Old 27-12-2017, 21:24   #15
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Re: Refrigeration system possibly overcharged...???

FWIW, I recently had that compresser clutch bearing replaced in my car's AC system for that very reason. Screeching when cold.
The mechanic who I employed said it could have easily seized, leaving me on the side of the road when the serpentine belt exploded due to being ripped asunder by a seized bearing.

Richard is right. Replace the bearing. It could very well be why the clutch is not engaging.

Actually, it probably is engaging, but to a temporarily seized shaft !
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