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Old 12-10-2011, 15:22   #1
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Proper Refrigerant Levels

We have a Coolmatic CU-55 on board and the instruction manual says nothing about proper psi for refrigerant. While the boat was on the hard this last winter it would appear that all of the refrigerant had leaked out. On the side of the unit it says Pressure: ND11/HD25 Bar. If you convert Bars to PSI then I should be charging my system to appx 160 Psi. This doesn't seem like a good idea. Most over the counter refrigerant refills only go to about 60 Psi any way. What am I missing? Does anyone know the proper Psi for one these units? We have it at 15 psi now and it seems like it is working ok but not great.
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Old 13-10-2011, 04:09   #2
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Re: Proper Refrigerant Levels

Just to keep it simple.
You may need to familiarise yourself with how a refrigeration system works. There is plenty threads in this forum about charging a system who may help you understand the working. Good technical book may also help. Good luck.
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Old 13-10-2011, 04:55   #3
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Re: Proper Refrigerant Levels

psi changes with temp.
perhaps the 160 psi is with the system running on the high pressure side

best way to charge is to weigh it in using a scale. If you know how many ozs refrigerant it takes.
The 15 psi your reporting is from the low side charging port? that sounds too low.
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Old 13-10-2011, 08:00   #4
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Re: Proper Refrigerant Levels

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Originally Posted by sdowney717 View Post
psi changes with temp.
perhaps the 160 psi is with the system running on the high pressure side

best way to charge is to weigh it in using a scale. If you know how many ozs refrigerant it takes.
The 15 psi your reporting is from the low side charging port? that sounds too low.
It doesn't appear that there is a high pressure side on this unit. At least not one that is accessible.
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Old 13-10-2011, 08:06   #5
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Re: Proper Refrigerant Levels

we have a frigoboat and it is a real low pressure system- 6-8 psi and it runs like a top - you may want to get a proper reefer mechanic on board and get it right and see what the proper pressure should be - then you can fiddle with it yourself

just our thoughts
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Old 13-10-2011, 08:25   #6
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Re: Proper Refrigerant Levels

I am not sure how you determined your system was low on refrigerant. If it was low did you find and repair leak? Adding refrigerant is not a solution by itself.
RULE Number 1. Never let any one connect gauges to one of these systems without conformation first that Danfoss BD compressor is actually running. Then never connect or disconnect gauges with compressor running.

That small unit only holds 50 to 80 grams of refrigerant. With thermostat set at mid range evaporator temperature will operate around 12 Degrees F. High pressure of liquid refrigerant will range from 105 to 120 psi depending on ambient air circulating around condenser and volume of refrigerant in system. To maintain refrigerant range temperatures inside evaporator from +5 degrees to 40 degrees low suction pressure with 134a refrigerant will be between 5 and 8 psi. Five psi suction would mean frosted all over evaporator. Eight psi suction would indicate a warm evaporator and little or no frost.

Pressures of 15 and 160 psi indicates too much or contaminated refrigerant, possibly air in system.
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Old 13-10-2011, 08:47   #7
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Re: Proper Refrigerant Levels

Quote:
Originally Posted by Richard Kollmann View Post
I am not sure how you determined your system was low on refrigerant. If it was low did you find and repair leak? Adding refrigerant is not a solution by itself.
I checked it with a guage and it read zero PSI. I did find and fix a leak. One of the nuts had vibrated itself off.
Quote:
Originally Posted by Richard Kollmann View Post
RULE Number 1. Never let any one connect gauges to one of these systems without conformation first that Danfoss BD compressor is actually running. Then never connect or disconnect gauges with compressor running.
What is a Danfoss BD Compressor? Doesn't this statement contradict itself? You just said never hook a guage to the system if it isn't running then you said never connect it or disconnect it with it running???
Quote:
Originally Posted by Richard Kollmann View Post
That small unit only holds 50 to 80 grams of refrigerant. With thermostat set at mid range evaporator temperature will operate around 12 Degrees F. High pressure of liquid refrigerant will range from 105 to 120 psi depending on ambient air circulating around condenser and volume of refrigerant in system. To maintain refrigerant range temperatures inside evaporator from +5 degrees to 40 degrees low suction pressure with 134a refrigerant will be between 5 and 8 psi. Five psi suction would mean frosted all over evaporator. Eight psi suction would indicate a warm evaporator and little or no frost.

Pressures of 15 and 160 psi indicates too much or contaminated refrigerant, possibly air in system.
I think what I am gleaning from all of this is that the indication on the side of the compressor (written on the side next to the model number and other specs) of 11 ND and 25 HD Bar is referring to the high pressure side.

I think you are saying that the low pressure side should be between 5 and 8 psi. And the a higher psi will yield a warmer temperature. Am I interpreting you correctly? The 15 Psi of refrigerant that we put in was an arbitrary amount that we chose just to get the show on the road. We had a delivery date picked and had to have cold beer.
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Old 13-10-2011, 09:00   #8
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Re: Proper Refrigerant Levels

Richard tends to assume you know more. Unless you know that the compressor actually works (runs) all by itself then you can connect a gauge set. Unless your unit has a dryer with a spyglass you will need a correctly calibrated refrigerant gauge set to measure and see what is happening.
- - When the system is running with a proper gauge set and refrigerant refill bottle/tank attached - then the "low side" pressures Richard lists will determine whether you need to refill the unit with refrigerant or not. Sometimes you will need to let some out if it has been "overfilled."
- - That "low side" pressure will set the temperature at the evaporator plates. This is where an experienced person with refrigeration is important - and - having the proper gauge set and fittings to service your unit.
- - Basically, too much refrigerant and the unit will not cool or get cold, too little and the same result. But in that narrow range of low side pressures you will go from no cooling to proper cooling to frosting over (too much cooling) and finally no cooling again.
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Old 13-10-2011, 11:32   #9
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Re: Proper Refrigerant Levels

Gotcha, thanks for dumming it down for me. The beer is cold and staying cold. Seems to be working ok, I guess I will leave it at that.
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