Last weekend I went to the boat with the proper equipment to repair a small leak on our front unit, a Marine Air 16000 btu VR16KH. After repairing the leak and pulling a vacuum for an hour it was time to recharge. A friend of mine is very good at this and coaches me via text messages and iPhone pics. When I appeared to be finished I used two quality analog matching probe thermometers. One in the return air register and one in the closest supply register per his directions. After running overnight I was showing a 20 degree TD (temperature differential). Wow! Awsome! Let me mention that by the time I checked that morning it was about 11:00 and the heat index in Biloxi was 111 degrees outside. Chuck said I needed to be sure I was not overcharged(280 psi HP)- as this could cause damage to the compressor over time. The data plate showed a value of 12 amps FLA (full load amps) on cool or heat. I put my clamp on amp meter over one leg and showed 13.6 amps. Too high! He had me check the blower amps (3) and then check all 3 wires at the compressor. 1 orange, 1 white and one black. I pulled the schematic out and saw the black wire came from the over heat switch. It had about 10.5 amps. I ended up removing a small amount of freon and watched the FLA drop immediately. I ended up at about 11.8 FLA. Checked my TD and I was down to about 11 degrees. HUGE difference! I slowly added freon in stages and finally settled on 12.15 FLA which gave me a 14 degree TD. High pressure was around 245. I was amazed at how close the line is between great cooling/ too many amps and decent cooling/ normal operating amps. I would encourage anyone charging their own system to get a clamp on amp meter and use this along with your gauges for proper settings.
First let me congradulate you for a job well done !!!
A few notes:
That FLA rating is with a clean water (condenser) coil & (I believe) 85* seawater...
<ul>[*]Seawater condensers are known to build up a hard water scale acting like an insulating blanket preventing proper heat transfer to the water...Similar to a dirty radatior in your car...[/list]Marine Air & Cruisair are designed for a 15 to 18 degree TD...So your 14* is a bit low.
Seawater temp, Ambient Air temp, Water Coil (condenser) condition, Evaporator Air Flow (Ductwork) & Incoming Voltage, all have an effect on Operating Pressures & Amperage Draw...So charging by amperage draw is not always the best option...
But your friend is right that overcharge is not good for the compressor.
I believe from your model this is a Split System ?
If so, It will have a piston type compressor...
<ul>[*]Compressor temp is controlled by refrigerant return (water only removes the heat from the refrigerant)*[/list]Compressor temp is most important...In A/C applications...You don't want it so hot you can't hold your hand on it...
<ul>[*]Too Hot meaning undercharged & not enough refrigerant return....[*]Too cold & sweating meaning too much refrigerant return and that the compressor is trying to compress liquid...[*]A overheating compressor cooks the oil and can seize...[*]A cold compressor (liquid) is washing away the lubricant, plus it's very hard on the valve plate causing a loss of compression, and or ability to pump the refrigerant.[/list]I can't really offer what the pressures Might be because of the above factors, but I will say that 250-260 psi head pressures in your climate are not uncommon during the high heat load times of day (even with a clean condenser)...Neither is higher than rated FLA...With a scaled up condenser they will run higher than that in a properly charged system.
Meaning that your 280 psi figure may not have been out of line...
Compressor Temp is a better means of charging, and that you are still looking for a minimum of 15 degree TD...If you have a proper temp compressor (warm) with a cold suction line, you will have a good idea the charge is correct for the conditions...If TD & pressures are then way out of spec...It's time to look at the above mentioned factors for the reason.
Note: This charging method differs for Rotary compressor self contained units...Rotary compressors do run hot by design...
-- Edited by spcoolin on Monday 13th of June 2011 02:36:38 PM