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Old 11-24-2012, 05:12 PM   #1
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charging in low temps


Hey Im working a water cooled heatpump (cruise air) I am not used to adding freon in low temp. Im in heat mode and it is working, but the compressor is really really hot. I tought I over charged it so I pulled it all out and started with 2 pounds. I think the think is 1.5 tons but that seems huge for a 40 foot boat. There is no charging chart or even a name plate.
Here are my pressures and temps:

od temp 50F
high side 240 and 175F
true suction 50 and 53F
indoor temp 56F
evap temp 93F
vent output 88F
water temp is about 65f

when I shut the system off it is 110 psi seems high to me for 50f DB.

Do these numbers sound right?

Thanks for the help

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Old 11-24-2012, 05:33 PM   #2
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charging in low temps


What's your superheat and subcooling. According to those numbers, you don't have any subcooling.

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Old 11-24-2012, 05:49 PM   #3
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charging in low temps


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high side 240 and 175F
true suction 50 and 53F
Corect me if Im wrong but
240 converts to 115 so that is 60 degrees
50 converts 26 so that is 27 degrees
Right?

Im just new to this in the winter

Once again thanks for the help
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Old 11-24-2012, 05:52 PM   #4
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charging in low temps


That is your high side pressure and your low side temp.
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Old 11-24-2012, 06:05 PM   #5
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charging in low temps


Im not sure what you mean, that is what I was using to calculate superheat and subcooling. That is what I am not sure of, in ac mode that is how I calculate it, is it not the same for heat mode.

Superheat is the difference of the evap temp (or converted suction psi) - the temp reading at the suction line, right?
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Old 11-24-2012, 06:12 PM   #6
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charging in low temps


what freon you using? Is there a name and model number on the comp?
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Old 11-24-2012, 06:15 PM   #7
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charging in low temps


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Old 11-24-2012, 06:32 PM   #8
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charging in low temps


this is a Marine system it is made by cruise air. There is no name plate, or charging charts. I see what you're saying now about the subcool, but there is lots of superheat which makes me think its under charged. but when the system is off it is 110 PSI which makes me think it is over charged on a 50 degree day. with no subcool wouldn't that mean its not rejecting the heat inside?

once again thanks for all your help
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Old 11-24-2012, 06:43 PM   #9
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charging in low temps


your off temp is because of the water temp, don't worry about it. Charge the thing to 15 degrees subcooling. All else being good, you should be fine. Subcooling is you high side saturation - liquid line temp.
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Old 11-24-2012, 06:45 PM   #10
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charging in low temps


no subcooling means there is no liquid in the high side coil to cool. Meaning you are low on refrigerant. the refrigerant is moving so fast through the coil that it is not being cooled.
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Old 11-24-2012, 06:52 PM   #11
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charging in low temps


What does a 50 degree day have to do with a water source heat pump.
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Old 11-24-2012, 06:52 PM   #12
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charging in low temps


I saw that and ignored it.
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Old 11-24-2012, 07:09 PM   #13
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charging in low temps


once again correct me if I'm wrong because I'm sure that I am, but I thought when an AC system has been all for sometime and all the pressures are equalized the psi converted to temperature should be the ambient temperature
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Old 11-24-2012, 07:29 PM   #14
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charging in low temps


it is going to convert to the highest temp it is exposed to. if the water temp is 65 then the refrigerant pressure will reflect that.
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Old 11-24-2012, 07:54 PM   #15
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Originally Posted by wetbar View Post
once again correct me if I'm wrong because I'm sure that I am, but I thought when an AC system has been all for sometime and all the pressures are equalized the psi converted to temperature should be the ambient temperature
The water is your ambient.

In heat mode the indoor coil is your condenser, and the coaxial is your evap.

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