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Old 04-11-2020, 05:54 PM   #1
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Question New AC, New pump, and MORE FROST!

Hello all. Long time no see.

Yesterday I installed a brand new Flagship Marine 18,000btu lowboy AC in the master stateroom. I used my existing pump which was a "Sea Choice," or the like, 500gph pump. I have no idea how old it was, the previous owner installed it.

After the install, everything worked. It cooled greatly. We started running it around 4pm yesterday, and at midnight it had froze over.

Using what y'all taught me, the first thing I looked at was my pump. I took it apart and although the magnet wasn't broken, there was some play in the impeller. I also thought it may have been undersized. So we went to "bend me over west marine" and paid $390 for a 1000gph Dometic pump.

I just got it installed, everything is working, I've got tremendous water flow, and its been on for about 30 minutes.

The bottom two coils that run through the fins have already exhibited signs of light frost. All the others above it are frostless.

Is this normal to have a bit of frost on the coils through the fins?

I was concerned about the amount of space between the AC and the bulkhead, so to make sure it got enough air I removed a piece of board that was installed for sound proofing . Just behind the red arrow in the photo below is a 18" wide return.

The only other issue that I have a concern about is the drain. The condensate drain is staying pretty full because the drain hole isn't at the bottom of the pan.

What else should I look at?
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Old 04-11-2020, 06:05 PM   #2
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Itís these coils. Toward the bottom.
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Old 04-11-2020, 06:32 PM   #3
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When I have seen frost on the coils is has been from lack of air flow. But I am not a HVAC guy.
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Old 04-11-2020, 07:07 PM   #4
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I'm not an expert on marine AC but know a bit about AC in general. It seems to me that if you were freezing the coils the problem is either airflow or evaporator temperature control. It seems evident that your compressor is working fine indicating that the condenser is cooling well (with either old or new water pump). If
it hadn't worked you wouldn't be able to freeze the coils because the refrigerant wouldn't be able to reject the heat. AC systems try to avoid frosting of the coils for any period of time because that causes them to ice up. This is normally done via either a thermal expansion valve that throttles the refrigerant or thermal cycling switch that cycles the compressor on and off. If your airflow is OK and you still frost up I'd wonder if there's a problem in the evaporator temp control
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Old 04-11-2020, 07:35 PM   #5
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Is that a solid panel to the right of the red arrow in the first photo or is there a grill there?
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Old 04-11-2020, 07:56 PM   #6
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It's most likely air flow.
Simple test:
Disconnect the discharge and the return air ducts. Then run the unit to see if you get frosting.

Ted
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Old 04-11-2020, 08:07 PM   #7
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Quote:
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Is that a solid panel to the right of the red arrow in the first photo or is there a grill there?
Itís set up like this under our bed.
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Old 04-11-2020, 08:10 PM   #8
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It's most likely air flow.
Simple test:
Disconnect the discharge and the return air ducts. Then run the unit to see if you get frosting.

Ted
I could disconnect the ducts from the dischaeg and just let it blow air into compartment.

Additionally weíve learned that this thermostat is about 4 to 5 degrees off. I guess because of the way itís mounted if we set it to 72 it runs until our salon shows 68 on my weather center screen. If we set it at 75 the salon reads 72.
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Old 04-11-2020, 08:22 PM   #9
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Quote:
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Itís set up like this under our bed.
But is the side to the right in your drawing a solid panel or is it a grill? If it is a solid panel that may be yout problem due to restrictive airflow.
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Old 04-11-2020, 09:00 PM   #10
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Quote:
Originally Posted by toocoys View Post
I could disconnect the ducts from the dischaeg and just let it blow air into compartment.

Additionally we’ve learned that this thermostat is about 4 to 5 degrees off. I guess because of the way it’s mounted if we set it to 72 it runs until our salon shows 68 on my weather center screen. If we set it at 75 the salon reads 72.
Ok, couple of things:
It looks like you have some serious return air flow restriction where the evaporator is to close to the wall. How big is the return air grate? When the air has to go through a small vent, squeeze between the evaporator and the wall, and then turn 90 degrees to go through the evaporator, you're going to get some flow restriction. Is it not possible to put the return air grate through the wall next to the evaporator?

Ted
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Old 04-11-2020, 09:01 PM   #11
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Open up the air flow as much as you can. If it is still freezing up, it's likely low on refrigerant and has a leak somewhere. Measure the temperature of the air just after it passes over the coil. the type of refrigerant will tell us what the normal temp should be.



I have had fjve out of six bad coils in Mitsubishi Mini Splits this year. Tech told me the Chinese had a bad run last year. All ran good for a day or two then slowly started freezing up!



Unfortunately some of the new systems use r410A that runs at a much higher pressure and will find even the smallest leak.


Hope the warranty is good.


Good luck.
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Old 04-11-2020, 09:03 PM   #12
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Quote:
Originally Posted by Comodave View Post
When I have seen frost on the coils is has been from lack of air flow. But I am not a HVAC guy.
Yup !
Make sure there are no links in the ducts.
Contact Flagship and tell them how many outlets and how many feet of duct work are involved. Lack of air flow sounds like the issue to me
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Old 04-11-2020, 09:13 PM   #13
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2 more things:
Check the installation manual for required return air vent size, it should be in square inches.

Measure the width between the evaporator and the wall next to it (it looks like 2 or 3"). Measure the height from floor to the top or the evaporator. Multiple the 2 numbers and see how it compares to required return grate size.

Ted
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Old 04-11-2020, 09:17 PM   #14
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Well, I turned the thermostat up to 75. That cools us down to about 72. And the frost has dissipated and the coils have returned to normal. It's not kicking on and off a little more normal, and the compressor doesn't sound like its about to take flight.

I'm thinking that because the thermostat is in the wall, and surrounded by a mounted plate, and covered in adhesive foam on the back it's not getting an accurate reading, and we were running it too hard.

As it gets warmer outside and we get closer to summer, I'll monitor it. If it gets to the point where it isn't performing optimally, I'll move it to the front which has a direct return in front of the grill, and move the smaller unit from the front to the back.
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Old 04-11-2020, 09:18 PM   #15
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O
Hope the warranty is good.


Good luck.

Better be. It was built to order about 4 weeks ago, and arrived on Thursday.
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Old 04-11-2020, 09:20 PM   #16
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Is it not possible to put the return air grate through the wall next to the evaporator?

Ted
No. I'd be cutting a hole in the wall allowing the ac to suck air from the bilge.
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Old 04-11-2020, 10:01 PM   #17
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Well you could run a duct from the hole in the wall to a return grill somewhere not in the bilge. Not as good but better than nothing.
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Old 04-11-2020, 11:18 PM   #18
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No magic - Flagship is a good product. Get one of these:


Amazon $15
Amgaze Anemometer Handheld, Digital LCD Backlight Wind Speed Meter Gauge


measure temp and air flow. I've seen these things running with 50% blocked evaporator air flow - dirty filters - blankets hanging over the intake -etc. Call Flagship ASAP. Coils should not be frosting up - at all While your return air is not ideal (most boats are not and Flagship knows that). Run it with the lid off the box - if it still frost up - its not air flow. It is a R410A based unit - they are very touchy with regards to refrigerant volume installed. the fact that its a brand new unit suggest a build problem.



If you've got good water flow, anywhere close to rated air flow, (the right things to check first)
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Old 04-12-2020, 01:48 AM   #19
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Damn it.

I'm going to have to switch the AC's and move the front one to the back, and the back to the front.

I just woke up, it's 1:47am, and it froze over again.
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Old 04-12-2020, 02:10 AM   #20
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Try to find a way to get more air to the return first.
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