Recent AC repair

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.

Most A/C units have a specific vacuum, measured in microns, that they operate at. They also operate with a measured amount of the proper refrigerant. If these requirements are met then the system can be properly analyzed. Putting a vacuum on a system for a period of time is usually to boil off any residual moisture left in the system after it has been opened. Then the pump is turned off to see if the vacuum can be held so that it can be determined if the system is leak free. The best way to know for sure is to place the refrigerant bottle on a scale and weigh the amount that goes in. Checking the amperage of the compressor is a diagnostic tool for a "quick" look at the system, but not an absolute. Adding or subtracting refrigerant to find a happy medium of pressure and amperage may indicate another problem. Your spec sheets from the manufacturer should show these requirements and everything should be done to meet those requirements. If the high side is high and the compressor amperage is high, this could indicate air in the system, too much refrigerant or a blockage in the high side. All of these will cause the compressor to work harder meaning high amperage draw. Not enough air flow across the condensor could also raise the head pressure.

Forkliftt wrote:
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.

Click to expand...

*Hi Steve~

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...

*

Steve~

Marine-AC.Com


-- Edited by spcoolin on Monday 13th of June 2011 02:36:38 PM

Hey Steve
Man- it's great to get "working knowledge". And thanks for the atta boy!
Great info about the seawater condenser. I might want to clean the system again soon. What is your preferred method?
Also, this is a non split system and the compressor has ways seemed to run hot. Do you think that is normal? Would love to add some more freon after cleaning the condensor. We went to the boat Friday PM and my amps were up a tad to 12.3- which seems to say no other leaks possibly?
Last question- this unit mounts in the front cabin beneath the lower bunk. The air enters the register in front of the unit and then gets pulled through the coil which faces away from the register. The unit has two supply air grills. One round one at the top bunk and the other is a rectangular one supplied by a flexible duct through the bilge and up and pointing to the ceiling near the lower helm. Is there a more efficient way to set this up?
Thanks!

Well like I said...If it's a Rotary compressor, charging is slightly different because it is normal for Rotary's to run hot...The hot discharge gas is just inside the compressor shell.

Most Rotary compressors are Tall & Skinny with the wire connections on top...

Most piston type comppressors are a bit Shorter but much Fatter, with the wire connections lower on the side...

Have you got a Fat compressor matey ??? *

As far as your install...It sounds about normal, but pictures, duct sizes & unit btu would help me comment more...

*

Steve~

Oops...That's right...You did say it was 16K...

From that I can tell you it needs a total of 80 square inches of discharge grill area & 140-160 of return...

Steve~


-- Edited by spcoolin on Monday 13th of June 2011 05:30:19 PM

Steve, I do have the wire connections on top. I think I am the proud owner of a rotary compressor!!
I will check my square inches. If I need to add a register can I put it low in front cabin?

Forkliftt wrote:
Steve, I do have the wire connections on top. I think I am the proud owner of a rotary compressor!! I will check my square inches. If I need to add a register can I put it low in front cabin?

Click to expand...

Skinny Dude *

*Depends on what you mean by "register"

Discharges should always dump out high because of the nature of colder air to fall...

You don't want Cold Toes & a Hot Head *

You may be better off if you have space...To enlarge one of the existing if needed...

Also: a 16K with 2 discharges as you described needs at least a 6 & 4 inch duct...Two 4's or even a 4 & a 5" won't do it...

*

Steve~*


-- Edited by spcoolin on Tuesday 14th of June 2011 08:12:51 AM

Thanks