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Marine-AC Topics
Troubleshooting
Mermaid AC trouble

Mermaid AC trouble
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Bill Thomas

4:51 pm August 31, 2010
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We have a 16,ooo btu Mermaid that has run great in my 34' San Juan sailboat for 11 years. Recently my water heater went out, with fresh water freely leaking from it, time for a new one. Well, while the AC was running I accidentally turned on the circuit breaker for this water heater(probably a direct short) and immediately it threw it's breaker and the breaker on the dock. After resetting both everthing seemed fine. AC came on and appeared to work, I left soon after, not really seeing if it still cooled, assumed it did. After returning a few days later and really needing the AC (100 degrees outside) everything on the AC ran but no cooling. Compressor kicks on, fan blows, water pumps no cool. Mermaid said if all the above works then it has lost freon do to a leak, time for a new AC. It seems coincidental to me that right after the electrical event I discribed that I would lose freon and a quick push on the low press. schrader valve revealed there was still press. The reset switch seems to be resetting.
Question, is their something I can look for that would have blown during this electrical event that is keeping the unit from operating?
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Steve Pooler

posts 1126

7:45 am September 1, 2010
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Hi Bill~

The only way I can think of that a short would have caused you to loose freon in that unit is if there was a bare or worn thru wire (connected to the W/H breaker) that was laying against some of the a/c tubing…When it shorted, it arked or grounded thru that tubing (like an arc welder) and burnt a hole causing the leak…

Pushing on the schrader will only tell you if freon is there…Not how much is there, and it only takes a small loss to cause the unit to stop cooling.

As far as I know and have seen on Mermaind units…The pressure switch is for High pressure & would not trip for Low pressure…

The only real way to tell what's actually happening with the A/C is to connect gauges & then run it…

Steve~
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Bill Thomas

12:57 pm September 1, 2010
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Thanks for your reply Steve, I will ask a friend to check with gauges. I was thinking that maybe it would be something electrical on the AC(not freon loss) as there had just been this short in the water heater circuit. None of the water heater circuit wires come anywhere near the AC unit.
Also, the reset switch(this unit is 11 years old) over time wouldn't pop out on its own as it did new and I had to pop it back out with my pocket knife. I have done this for years, but do you think I should replace it? Can I just bypass it to test?

Thx, BT
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Steve Pooler

posts 1126

1:30 pm September 1, 2010
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The only reason the reset button should pop out in the summer is if the unit is run without water flowing thru it…

I guess I'm not understanding why you would need to pop it out with your pocket knife ???

To test it…Shut off or disconnect the pump…It should pop out on it's own within about 30 seconds (max)…Unless the unit is low on freon, in which case the compressor will not be able to build up enough pressure to make it pop out (it takes around 425 internal psi to make it trip)

Sounds like you may have been loosing freon (at a slow rate) for quite some time…Now there is not enough for it to cool at all.

The water heater failure is likely just coincidence.. 

Steve~
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Bill Thomas

9:06 am September 2, 2010
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Thx Steve, when I do this test, if the reset does pop out does that mean I don't have a freon loss? I will also try to put gauges to it.
BT
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Steve Pooler

posts 1126

9:12 am September 2, 2010
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Not really BT…It just means there is enough freon for it to build up 425 psi with no water flow…And that the pressure (reset) switch is good  Wink

Steve~
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Bill Thomas

8:43 am September 4, 2010
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425 psi isn't enough to cool? At all?
Thx, BT
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Steve Pooler

posts 1126

9:07 am September 4, 2010
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Bill~

What I'm saying is…The reset button is a manual reset for a high pressure switch which is calibrated to trip/pop out at 425 psi…

It's purpose is to protect the compressor & other parts from high pressure if you you loose water flow…loss of water flow will cause high pressure…

If slightly low on freon (low enough for no cooling with water flow) it could still build up enough pressure to trip the switch with no water flow…However if it is really low on freon, there may not be enough to build up to 425 psi (without water) so the test may not pop the reset.

You still need gauges & someone with knowledge to know what is really happening/preventing the unit from cooling…I only mentioned shutting off the water as a test because you brought up the reset…This would only be a test that the reset worked as designed…not that the unit was full or not full of freon…However, again if it is really low it's not a good test of the switch.

Steve~ 
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