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Old 12-27-2018, 04:10 PM   #1
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A/C heating issue?

Hy everybody, on my ST44 i noticed that while the saloon a/c in heat mode blows out pretty hot air, the two staterooms units don't. The air flowing out in the master stateroom is nearly cold, and the room temp never goes over 15 degree C.
The water flow seems good: any suggestion?
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Old 12-27-2018, 04:58 PM   #2
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Are the two state rooms on a separate system? If so the most common cause of no heat on a reverse cycle system is a stuck switching valve. Bang on it lightly with a hammer and see if it doesn't start heating.


The switching valve has three, maybe four tubes in and out of it and wires to a solenoid built in the the valve. It is near the compressor.



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Old 12-27-2018, 05:03 PM   #3
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Thanks djmarchand, will try tomorrow.
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Old 12-27-2018, 07:16 PM   #4
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Originally Posted by djmarchand View Post
Are the two state rooms on a separate system? If so the most common cause of no heat on a reverse cycle system is a stuck switching valve. Bang on it lightly with a hammer and see if it doesn't start heating.


The switching valve has three, maybe four tubes in and out of it and wires to a solenoid built in the the valve. It is near the compressor.


David

What David said, but I'd take exception to the hammer. Those valves are fabricated from copper and brass, if you bang on the wrong place with a hammer, it could be TU for the valve. My persuader of choice is the handle of my biggest screwdriver. Those capillary tubes are copper, robust they are not, so go lightly. Changing out a reversing valve is true joy. (NOT!!)






A less risky approach might be to find the connection for the solenoid that shifts the valve. The solenoid doesn't actually move the valve, it's a pilot that ports pressure through those little cap tubes and the pressure is what causes the valve to shift. Sometimes the valve can be coaxed into submission by cycling the solenoid while the unit is running (heat). Just carefully remove one of the power leads (they're usually line voltage) and the valve should shift. Careful not to ground the lead against the refrigerant tubing! It'll make a pressure-relieving whoosh if it's working properly. Shift it back & forth a couple of times, give it time to rebuild pressure between- it won't damage anything. Incorporate a few judiciously applied taps if it seems balky, try to go for steel parts that won't deform- like the steel frame of the solenoid or the ends of the valve, depending on how they're fabricated.
There are also check valves in other parts of the refrigerant circuit, they could also be contributing if they're balky, that's why I like shifting the valve under pressure, it shakes those check valves loose, too.
One additional note, most marine systems energize the solenoid in heating, e.g. in cooling they're de-energized. So if nothing happens when the power lead is removed, it may be that it's powered in cooling, and you'd have to run for cooling to accomplish the cycling. Residential systems are typically configured to fail in heating. If you're proficient with a ladder diagram, you can determine how it's controlled, but it's either one or the other, shouldn't be to difficult to determine which.
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Old 12-28-2018, 01:02 AM   #5
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Thanks Maerin. Very useful explanation!
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Old 12-28-2018, 06:52 AM   #6
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Originally Posted by Roidagobert View Post
Hy everybody, on my ST44 i noticed that while the saloon a/c in heat mode blows out pretty hot air, the two staterooms units don't. The air flowing out in the master stateroom is nearly cold, and the room temp never goes over 15 degree C.
The water flow seems good: any suggestion?
On the ST44 the two stateroom units share a raw water pump. If raw water is flowing then the pump is working. What is the water temperature? Air temperature in the stateroom? Temperature of the air coming out of the vent?

Have you looked at both units to see if they are frozen? How long are you running them before checking for hot air? What temperature are you setting them to?

Its possible you have a 16k btu in the salon which will get a lot hotter than the 8k btu in the staterooms.

How old are the units? If more than a couple years, have you done a flush?

Regarding a stuck reversing valve, try going into AC mode then heat then back and forth a few times letting the reversing valve click. You can hear it switch if its working.
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Old 12-28-2018, 08:05 AM   #7
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I suspect many reverse cycle systems never get run in heat mode, so there is a possibility that the reversing valves arenít wired for those other units. Itís a bit of a stretch, but worth a quick check. A meter in the electrical connections at the valve should confirm one way or another
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Old 12-28-2018, 09:09 AM   #8
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Not sure which controls you have but some have programmable parameters related to their function. Might double check yours to insure that is not an issue causing your trouble.
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Old 12-28-2018, 10:50 AM   #9
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I suspect many reverse cycle systems never get run in heat mode, so there is a possibility that the reversing valves arenít wired for those other units. Itís a bit of a stretch, but worth a quick check. A meter in the electrical connections at the valve should confirm one way or another

I doubt if any reverse cycle A/Cs are intentionally shipped that way from the manufacturer, but I did have one system in a new boat where the wires had come loose. Easy to diagnose- just look or check with a meter and to fix.


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Old 12-28-2018, 11:33 AM   #10
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I doubt if any reverse cycle A/Cs are intentionally shipped that way from the manufacturer, but I did have one system in a new boat where the wires had come loose. Easy to diagnose- just look or check with a meter and to fix.


David


Iím thinking of an installation screw up that went undetected until someone actually tried to use the heat.
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Old 12-28-2018, 11:56 AM   #11
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Originally Posted by Roidagobert View Post
Hy everybody, on my ST44 i noticed that while the saloon a/c in heat mode blows out pretty hot air, the two staterooms units don't. The air flowing out in the master stateroom is nearly cold, and the room temp never goes over 15 degree C.
The water flow seems good: any suggestion?
Stuck reversing valve is the first guess (as others have noted). My owners manual (Dometic) actually DOES say to tap on the reversing valve to fix the problem!



Another thought -- reverse cycle operation needs significantly higher compressor head pressures than cooling mode. In Dometic (MarineAir) units, they actually reduce the fan speed in reverse cycle mode to increase head pressure. If you are in a cold climate (water temp less than 55 degrees) you can expect the unit in heat mode to require a significant amount of time to start making heat. In my experience, the larger (16K BTU) units start making heat MUCH more quickly than the smaller (8K to 12K BTU) units. I can't say why this happens, but that's my experience over many years.


Last thought -- if your units are getting old, it may be that there is enough life left in the compressor/seals etc. to work O.K. in cooling mode, but not in heat mode. It makes sense to me that if your compressor(s) are marginal or if refrigerant charge is low, then the first symptom you might notice would be poor performance in heating mode.
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Old 12-28-2018, 12:16 PM   #12
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Thanks everyone.
My ST44 is new (2 months) so I'd rather have a pro check for problems than void the warranty
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Old 12-28-2018, 12:52 PM   #13
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Heck, if itís under warranty, call Beneteau or Dometic
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Old 12-28-2018, 02:10 PM   #14
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Not sure which controls you have but some have programmable parameters related to their function. Might double check yours to insure that is not an issue causing your trouble.
Had exactly the same issue. An HVAC guy told me to hammer on the valves too. Seemed like a big risk with all that soft metal involved. Our Airrrrrrr controllers for Dometec units have three choices, Heat only, AC only, or Auto. I have to keep getting the book out to remind me how to change them into the correct mode. Once set correctly they run fine. All share one sea water pump.
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Old 12-29-2018, 10:16 AM   #15
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Thanks everyone.
My ST44 is new (2 months) so I'd rather have a pro check for problems than void the warranty
Can you answer the questions I posed please? You may not need to waste your time with a pro.

PS. even in warm climates/summer, its good to run heat mode at least once every month to keep the reversing valve exercised. Only need to do for 30-60 seconds. I usually go from AC to heat, wait to hear the click, wait 30 seconds, back to AC, click, wait 30 seconds, back to heat, listen for click, and then back to AC. A little back-and-forth is good.
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Old 01-07-2019, 03:37 AM   #16
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On the ST44 the two stateroom units share a raw water pump. If raw water is flowing then the pump is working. What is the water temperature 14 C ? Air temperature in the stateroom? 8C Temperature of the air coming out of the vent? Dunno

Have you looked at both units to see if they are frozen? Yes, thy are ok How long are you running them before checking for hot air? One our What temperature are you setting them to? 20C

Its possible you have a 16k btu in the salon which will get a lot hotter than the 8k btu in the staterooms. NO

How old are the units? If more than a couple years, have you done a flush? THE BOAT IS NEW

Regarding a stuck reversing valve, try going into AC mode then heat then back and forth a few times letting the reversing valve click. You can hear it switch if its working.
You find answers up in the quote
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