New AC, New pump, and MORE FROST!

[toocoys]

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?

 

[toocoys]

It’s these coils. Toward the bottom.

 

[Comodave]

When I have seen frost on the coils is has been from lack of air flow. But I am not a HVAC guy.

 

[Slowmo]

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

 

[Comodave]

Is that a solid panel to the right of the red arrow in the first photo or is there a grill there?

 

[O C Diver]

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

 

[toocoys]

Is that a solid panel to the right of the red arrow in the first photo or is there a grill there?

It’s set up like this under our bed.

 

[toocoys]

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 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.

 

[Comodave]

It’s 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.

 

[O C Diver]

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

 

[Olebird]

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.

 

[boatpoker]

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

 

[O C Diver]

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

 

[toocoys]

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.

 

[toocoys]

O
Hope the warranty is good.


Good luck.

Better be. It was built to order about 4 weeks ago, and arrived on Thursday.

 

[toocoys]

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.

 

[Comodave]

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.

 

[Olebird]

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)

 

[toocoys]

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.

 

[Comodave]

Try to find a way to get more air to the return first.

 

[Comodave]

Is there any space to the left in the first photo? If so can you slide the unit to the left any? Every little bit may make a difference.

 

[toocoys]

Try to find a way to get more air to the return first.

I have ample amount of room to put a fan between the grill in the wall, and the unit, which would pump more air into the hatch and improve airflow.


I guess my next test should be to lift up the mattresses, open the hatch and let it run for a while and see if that solves the issue.

I'll have to contact Steve at Flagship on Monday and see what he says.

 

[toocoys]

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.

Well, it may have sustained damage. I did forget to mention that this is what it looked like when it came off the truck. I did let Flagship know immediately but the unit didn't look like it sustained damage.

 

[O C Diver]

How long is the supply duct, what diameter, how many turns, what size grill on the end? Are the supply ducts from a previous AC that was a lower BTU? Try taking the grill(s) off the supply ducts and see if you perceive more air flow.

Ted

 

[ranger58sb]

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.

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.

Once you get the main problem solved... maybe the thermostats are adjustable? (Ours are, but it's a different brand.)

When our new units were installed, the tech said something about fan speeds and freezing. This because we have a bit of adjustment available in upper and lower fan speed limits, and I was asking about changing from the defaults. My intention was to widen the upper-lower limit to get the most variation from each fan speed setting.

I don't remember exactly what he said, but I think it was about not setting the lower fan speed limit to it's lowest possible setting... because of a tendency for that to cause freezing. I didn't understand what he meant, and just glossed over it anyway, but... I mention it in case fan speeds might be germane to your freezing issue.

-Chris

 

[toocoys]

How long is the supply duct, what diameter, how many turns, what size grill on the end? Are the supply ducts from a previous AC that was a lower BTU? Try taking the grill(s) off the supply ducts and see if you perceive more air flow.

Ted

The supply duct is 6" coming off the unit. It has a 1 to 2 foot turn to a register box that has another 6" and a 4" duct connected to is. The 6" duct runs aboue 3 feet up the wall to a double sided vent thats about a foot long and 6" high. Air blows into the salon and into the master berth from this duct. The 4" duct has about a 10 foot run into the master head that has a 4" circular vent in it.

 

[toocoys]

I put a fan in the hole in the bed, where the AC should theoretically pull air into. My thought was to pump more air into the compartment for the AC to take in. Unfortuntately that didn't work either. It still frosted over. I turned everything off before it fully froze again.

 

[FF]

One frosting cause can be an overfill of the refrigerant.

 

[Pete Meisinger]

I think most cities have a "junk" store, unclaimed freight, Axman (in Minneapolis) etc. Pick up a computer cooling fan. They are silent, move quite a bit of air and can be wired to come on with the compressor. Maybe you could get one from a computer repair person also.

You need more airflow. You may have to duct some air into the compartment or move a wall or something.

pete

 

[O C Diver]

The supply duct is 6" coming off the unit. It has a 1 to 2 foot turn to a register box that has another 6" and a 4" duct connected to is. The 6" duct runs aboue 3 feet up the wall to a double sided vent thats about a foot long and 6" high. Air blows into the salon and into the master berth from this duct. The 4" duct has about a 10 foot run into the master head that has a 4" circular vent in it.

Does the register box have a grill vent putting air conditioning into the room?

Boxes are poor as distribution tees because they develop turbulence which slows air flow down. A "Y" or smooth pipe "T" is much better as it generates little turbulence.

A 10' run with a 4" circular vent was little air flow as the 4" diameter tube generates lots of static line loss (resistance).

Was the duct work existing from a smaller BTU air conditioner?

IMO, not enough square inches of vent, too small ducting that has too long runs, and your distribution box is generating turbulence resistance.

Have you tried running the system with the supply vents removed?

Ted