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AC help and it is hot!

Old 06-11-2010, 07:45 PM
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Default AC help and it is hot!

AC was freezing up so I had the guys come out and take a look. They said it was
low on refridgerant and added to it. Now the AC compressor will come on run for
30 seconds and the high pressure switch kicks it off. According to Mermaid the
ONLY thing that would cause that to happen is poor or no water flow. We I can
tell you with my own eyes I have a ton of flow and it is happening...of course
it is going to be 90 degrees tomorrow.

Any ideas on what the heck may be going on?
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Old 06-11-2010, 07:52 PM
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So get them back out there! They obviously didn't do a full system check...and it's on their dime!
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Old 06-11-2010, 08:05 PM
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What bob says. Don't know if you misunderstood Mariner or what, but I'm pretty sure there are a number of other things that can cause HP switch to pop.......overcharge for one, different blockages in the system for another. As bob said, I'd invite the tech back.
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Old 06-12-2010, 04:35 AM
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Originally Posted by seabob4 View Post
So get them back out there! They obviously didn't do a full system check...and it's on their dime!
Isn't that the obvious ?

BTW: No repair person is going to be happy with you when you tell mim that people on a boating forum said that the problem was .................

Tell them what it's doing and let them fix it.
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Old 06-12-2010, 01:10 PM
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One of my units did exactly the same thing...bad pressure switch, new switch, problem solved. You need a good tech who works on them all the time, they are pretty simple.

good luck!

Randy
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Old 06-12-2010, 04:04 PM
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In the meantime you can clean out the raw water lines. Open your Strainer and put a few small bleach tablets in the strainer. This will kill any growth in the cooling lines. Marine growth (algae and slime) will accumulate in the cooling coils, preventing the unit from cooling causing the High Press Sw will shut it down. Happens a lot when surface water temps are high and units sit longer periods without running. Even if you have good volume of flow, if the water is warm and the growth impedes heat transfer, it will not cool.

Good chance this is your problem. Worth 20 min to check it out.

Last edited by 54bullwinkle; 06-12-2010 at 08:06 PM.
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Old 06-13-2010, 06:45 AM
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Originally Posted by Painintheaft View Post
AC was freezing up so I had the guys come out and take a look. They said it was
low on refridgerant and added to it. Now the AC compressor will come on run for
30 seconds and the high pressure switch kicks it off. According to Mermaid the
ONLY thing that would cause that to happen is poor or no water flow. We I can
tell you with my own eyes I have a ton of flow and it is happening...of course
it is going to be 90 degrees tomorrow.

Any ideas on what the heck may be going on?
Did you tell Mermaid that someone had been out to charge the unit, and/or were they Mermaid guys ?

Yes...Poor water flow or a dirty (scaled up) condenser could, and often does cause Hi pressure shutdown...But...

The fact that the unit was icing is not always due to low freon...It can also be an Air flow problem as simple as a clogged return filter, or a cold air duct leak blowing back onto the evaporator coil...
Both of these problems might cause a guy to keep adding freon after the system is full...trying to keep the suction (low side) pressure up above the freezing point....(about 58 psi with R-22)

Now with the unit overcharged...When it cycles off and sits for a few minutes the refrigerant pressures equalize thru the cap tube...
When the unit starts again with too much refrigerant it can't pump it all thru that cap tube and builds up the high pressure & shuts off...

I believe Mermaid is still using a "Manual Reset" High Pressure Switch (if you don't have digital control)...

Not that I recommend it and I only say this to confirm the above assumption of overcharge...But you could likely get the unit to run if to stayed close to the pressure switch reset button & after about 10 seconds of off...re-set it...If it pops again...Wait 10 seconds & try again...

If it then runs without tripping the reset...The unit is way overcharged, slugging liquid refrigerant thru the compressor & freon loss was not likely your problem in the first place.

I reiterate...Only do this as a test to confirm overcharge !!! Do not continue to reset just because you are hot...Running this way will damage the unit !...Plus you will need to sit next to the reset button every time the unit cycles...

Get someone back out to do the right job & find the original problem...

Below is a short article I wrote on my site about system icing...
http://marine-ac.com/2009/07/16/ac-system-ices-up/

Steve~

Last edited by spcoolin; 06-13-2010 at 08:54 AM. Reason: Added article link
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Old 06-13-2010, 06:41 PM
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An iced condenser is caused by lack of airflow, not lack of water flow. Clean the filter and make sure nothing is blocking the return air path. If not enough air is flowing across the coils they get too cold and the condensation on the coils freezes and that blocks the airflow completely. Does your unit have an de-ice mode? If so, make sure it is turned on. This mode engages the reversing valve, putting the unit in heat mode for a fixed length of time. This melts the ice but if the original problem persists, it will just freeze up again.
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Old 06-13-2010, 06:52 PM
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If you have good air and water flow and it still shuts down on the high pressure switch, there are a few different things that can cause that. Bad switch // overcharged with refrigerant // restriction in refrigeration circuit.
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Old 06-13-2010, 08:10 PM
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Originally Posted by spcoolin View Post

Yes...Poor water flow or a dirty (scaled up) condenser could, and often does cause Hi pressure shutdown...But...

Steve~
Hey Steve,

First of all thanks for all the valuable info on your site and your responses here. I have a similar issue...

My MarineAir system is getting a HPF. I'm sure its growth in the lines. I have to clean the strainer every 2-3 weeks during summer. However, last summer the boat was new and the A/C worked great even in hot weather. Water flow seems to be pretty strong though. Its definitely not visibly weakened.

I tried your suggestion in another thread of tapping into the input with a brief (15-20 min) soak with 50/50 muriatic/water. That helped for a while but on super hot days it still cuts out.

So I bought a used TRAC port o flush junior. I'm sure it works well but I'm glad I didn't pay $350 for it, as its a pretty basic bilge pump mounted in a 5 gal bucket. ;-) I'm guessing $70 in parts tops.

Anyways, do you recommend running muriatic through this? If so, what mix and how long? They only say to run their product, Barnacle Buster, but I'm wondering if thats necessary or just marketing. :-)

Also, I read on your site that some folks have been trying copper fittings in the strainers. I put a small copper pipe fitting in during my last strainer cleaning. Just wondering if you have seen success with that or if there are any downsides?

Thanks.
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Old 06-14-2010, 09:11 AM
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Same problem i had a low battery, one of the breakers on the inboard charge tripped and i didnt notice it until it was really low. that battery ran the water pump.
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Old 06-14-2010, 09:24 AM
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Also, just because you have what appears to be good water flow doesn't always mean that the tubes are all clean...you can have flow over a layer of scale and growth which will inhibit the energy transfer significantly. The post above about the Trac flushing system is good, but you can do the same with a 5 gal. bucket and a cheap $40 submersible sump pump from Lowes or HD. Over the weekend I flushed all 3 units and it was amazing what came out the back end....I used Starbrite's DeScaler, it was a bit cheaper than the TRAC stuff.
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