Steve,  

Back again after prior posts originating on 6/5/11 and 7/18/11 to this forum.  

Have 2, CM16 H units in Cambria 44 foot sailboat, original install in 1986.  One March AC-5C-MD pump [new 7/11] feeds both units.  One, 2PRP relay.  Both units have their own three knob cabin control units.  Each unit has own breaker, and water pump has its own breaker.  Location:  Massachusetts. Water temp:  about 70 degrees F.  

Both units had been cooling well since water pump replacement in July.  Now starting to use heat.  Forward unit works fine. Aft units works well, but trips its breaker after about ten minutes.  Water stays on — does not trip.  Good water flow forward and aft. Strainer clean.  Air filters clean.

Please advise!

Thanks in advance,  George

Steve,   Very helpful as always.  I will check all duct connections.  Some of the aluminum fins on the air intake for the aft unit looked like they were distorted at some point in the past.  I only use that aft unit on the highest fan speed.  The reason for that is that the fan on the aft cabin unit has always seemed to run much slower than the fan on the forward unit.  I don't know if that was the way it was designed or if the slow fan speed is a symptom of some type of problem.  Except for the slow speed that fan sounds normal.  In the five years we have had the boat with these units the aft unit has always had this slower fan speed, but has performed well, until now. 

Many thanks, George

GeorgeH said:

Steve,

More info:  Ducting looks to be secure — all 5 inch diameter.…Ok, But what BTU is that air handler ???…5" duct is only large enough for 8 or 9K…16K requires 7" duct…I removed the three knob control unit for the unit in question, and I see that some of the connectors on the back of the off/start/run knob, and also the warmer/cooler knob look burned...Yes, this is indication that you are drawing high amperage… Wiring looks okay.  I have photos of this I can send, but could not figure out the upload procedure. Thanks again. George

 

George~

As I described in my last post…Restricted air flow causes high pressure in heat…This high pressure causes the compressor to work harder pumping against that higher pressure & thus draw higher than normal amperage doing so…

Does this control/compressor operate more than one air handler ?…If so…Then that could explain your statement about the aft air handler not moving much air…It may be smaller than the other one connected to that system…If the system is 16K…The total BTU of both air handlers should equal 16K since you have a 16K compressor.

You could have a Larger AH fwd & Smaller aft…Like 12K fwd & 4K aft…Or 10K & 6K…

If this is true then the Fwd 10 or 12K unit should have 6" duct & 4" or 5" on the smaller aft unit…

It is very common for Boat builders to under size ductwork…The problem shows most in the heat mode, but can also cause icing in cooling…This icing might make a service guy overcharge the system in an attempt to keep the system from icing in cool mode….But that overcharge will only compound the problem in heat mode…

 

Air Flow is "ALL IMPORTANT" in Direct Expansion Air Conditioning…

 

Steve~

Post edited 5:41 pm – October 4, 2011 by Steve Pooler

George~

I must admit that I have always been a Cruisair guy first…I worked for the distributor here for 10-11 years before the Cruisair Marine Air merger (started there in 87)…I did work on all brands, but didn't pay much attention to competitors model/part numbers…We always replaced with Cruisair parts/units as many were a copy/exact match with Cruisair parts.

I have been thinking your CM 16H units are split/remote systems (where the air handler is separate from the compressor)

If you are saying that they are All in One "Self Contained" units that's fine & I learned something….…But now that I think of it…Marine Air did call their Self Contained line "Cabin Mates"…With Cruisair it was (and still is) "Stowaways"

Your model CM-16H likely stands for Cabin Mate 16K with Heat…

Still…If they are 16,000 BTU self contained units….That makes the answer that much easier…5" duct IS your problem.

16K units Require 7"duct (at least Cruisair's did, and now Marine Air does the same)…Although back then we did see Marine Air 16K units installed with 6" duct (which was too small)

A Cruisair 12K unit of that vintage (with 6" duct) would perform as well as a Marine Air 16K would…In fact we used to replace bad Marine Air 16's with Cruisair 12's if the owner did not want to go to the expense of up-sizing/changing the duct & grills…We do the same today…Replace 16's with too small ductwork, with 12k units…Customers swear they have never had Better or Quieter performance…

Again…5" duct is only good up to 8000 BTU (maybe an older Marine Air 9K but they now make a 8K instead) the next unit up is 10K and even it requires 6" duct.

A way you can test/prove my statement/s is to completely disconnect the duct from the blower to see if the problem go's away (just make sure the warm/hot air does not reflect back to the units return)

The hole you describe in your fan speed control is for a small flat blade screwdriver to reach inside & adjust the low speed pot…You can set how low is low speed…High speed is non adjustable.

Steve~ 

Thanks again Steve,

Yes, two Cabin Mate units.  The LRA # is 72.5 on the aft unit compressor.  Does that let you know the BTU rating?  I will disconnect ducting from blower and test, but is it okay to run that unit given the burned looking wire terminals I described before?  Also, shouldn't I see about solving the low fan speed on this unit?  [At present the fastest fan speed on the aft unit is even slower that the slowest fan speed on the fwd unit].  

George