Heat Not Working Randomly

jaywoodz

jaywoodz

Member
Nov 12, 2012
522
Richmond, Virginia
Boat Info
1999 Sea Ray 310 Sundancer
Engines
Twin 350 MAG MPI Horizon w/V-Drives
After replacing my unit completely 2 years ago, my AC and heat have been perfect. I recently moved to a different marina, and have the opportunity to run my heat/AC often, without a large electric bill. Over the past 2 weeks, it's been colder here, so I've set my heat to run and stay at 65. There was only 2 nights where it reached under freezing, and most days have been mid-40s/50s.

Today, I was working on the boat, laid to down to relax and watch TV. I noticed, that my heat started blowing cold. I thought it was strange, as it was just blowing heat keeping the cabin at 68 while I was working in and out of the boat. I did what anyone else would do, and reset the breaker, waited a couple minutes, then started the heat back again. Sure enough, it blew cold. I have a cruisair unit.

I decided to leave the breaker on, and simply "turn off" the heat. Waited a few minutes, then turned it back on - still cold. I set it to dehumidify, let it run for about 10 minutes, then set it back to heat - still cold. I cut the breaker off again, waited 5 minutes - cut it back on - cold.

I've run out of options for basic troubleshooting, and concluded that perhaps I'm low on freon? I'm not an AC/heat pump expert, but I own a few homes and seems to have been the issue in the past.

Either way, other than calling an AC/heat guy (not sure who else I could call to troubleshoot).. what else can I do? Perhaps try again tomorrow?

In case anyone is wondering, there IS water being pumped through, and coming out the side of the boat - there isn't a stoppage. One thing I've noticed in the past, when I cut the breaker off to the AC/heat, it lets out a loud "whooooosh" as if air is leaving the compressor. It did NOT do that any of the times I reset it today through my steps of troubleshooting.

Any help would be appreciated!
 
Is the compressor running and blowing cold air when in cooling mode? - A good rule of thumb is the diferential in the ambiant air temp at the return and the air coming out of the ducts should be at least 15-20deg. If the cooling seems to be working, but just won't switch over to heat, it is likely the reversing valve. The Cruisair's work just like a home heat pump, just use water to exchange the heat. It literally runs one way in cooling mode and the reverse in heating mode, there is a valve that reverses the freon flow and it can get stuck, a tap with a hammer will often get the valve working again. If cooling is not working, then you are likely low on freon - but seems you would see a low freon code on your display.
 
BillK2632 said:
Is the compressor running and blowing cold air when in cooling mode? - A good rule of thumb is the diferential in the ambiant air temp at the return and the air coming out of the ducts should be at least 15-20deg. If the cooling seems to be working, but just won't switch over to heat, it is likely the reversing valve. The Cruisair's work just like a home heat pump, just use water to exchange the heat. It literally runs one way in cooling mode and the reverse in heating mode, there is a valve that reverses the freon flow and it can get stuck, a tap with a hammer will often get the valve working again. If cooling is not working, then you are likely low on freon - but seems you would see a low freon code on your display.
Click to expand...

Yes, I can hear the compressor kicking in whether it's heating or cooling. Obviously when cooling, it's blowing cold air, but it's cold outside, so that doesn't mean much. Heat also blows cold air - I don't know if there's a difference in temp between the two. I have a soft mallet that I can use to hit the compressor - how hard should I "tap" it?
 
Its not the compressor that needs hitting, its the reversing valve. It is usually down low it the pan area. Take a look at your manual, it should show it.
 
I just researched this, and looked deep in the manual. Searched the whole thing, and it never actually labeled the "reverse valve".. here's a pic of what I have:

This is the "newer" model of the one I have, but it's almost identical.
dometic_dtu_9108893531_44977_11.png
 
Yes that's it. Tap it with a rubber mallet, not too hard you don't want to damage any of the copper tubing. Might need to tap it and switch from cool > heat a few times.
 
BillK2632 said:
Yes that's it. Tap it with a rubber mallet, not too hard you don't want to damage any of the copper tubing. Might need to tap it and switch from cool > heat a few times.
Click to expand...

I tapped it - no luck. I can't really tap it good, because my rubber mallet isn't small, and can't really get in there to hit it directly, so I've lightly tapped the parts connecting to it. I tried switching on and off a few times, switching from heat to cool. I even set up a heater near the intake at the foot of the bed, so the thermostat can rise in temp, and turn on cool, and actually blow cold.

No matter what I do - it blows cold.
 
I have tested that the AC is *working* - when I set a heater at the thermostat, it does blow colder air. I tested this with a thermometer. So, it's really just the heat not working.

I've noticed that there is condensation, then eventually ice on the lines of the unit. This is after running it on the "heat" cycle for about 15 minutes.
 
This is what it looks like after running the heat (still blowing cold):

Keep in mind, when this randomly started blowing cold.. the heat had been running fine for weeks.. I never switched it to cool, it's been on heat for a while. So if it's the reverse issue, I feel like it would have been because I switched it from cold to heat, and it not work.. but it's been working fine for a while now. If running heat, can it just shift back to cool for no reason? without being triggered to go cool?

IMG_0100.jpg
 
Its possible you have a bad thermostat, maybe not telling it to switch to heat. If you have 2 units, try switching thermostats, if not maybe someone on the dock has a similar they will let you try.
 
bahamabreisus said:
Its possible you have a bad thermostat, maybe not telling it to switch to heat. If you have 2 units, try switching thermostats, if not maybe someone on the dock has a similar they will let you try.
Click to expand...

When the temp gets low, the heat "kicks in" and I can hear the compressor. The temp on the display goes up and down as I set or remove my portable heater in front of it. I think the thermostat is working since it "kicks in", and the cooling happens as I stated earlier in the post.

That means the thermostat is working, right? I only have one unit so I can't take it out of another one.
 
Last edited:
When those lines ice up like that it is indicative of being low on refrigerant, aka Freon. You can check the high and low pressure sides with a set of Refrigeration Gauges or get your mechanic/AC technician to do it. I had to do this on my boat last year. An AC check and fill was $250.

Jaybeaux
 
Like Jaybeaux mentioned, the icing lines can be an indication of low freon, but also insufficient airflow across the coils or low flow the water pump - it might be time to to call someone in to look at it.
 
BillK2632 said:
Like Jaybeaux mentioned, the icing lines can be an indication of low freon, but also insufficient airflow across the coils or low flow the water pump - it might be time to to call someone in to look at it.
Click to expand...

Could be - I verified, and double verified that good water flow is coming out of the boat pouring into the river.
 
Third Edition said:
Is the filter clean? That can restrict airflow, of course.
Click to expand...

I cleaned the strainer last night - it actually wasn't bad at all. No debris, just muck from the river, and brown staining. 30 seconds in the sink with water and cleaner, and it was good as new. I even stuck my hand in there to ensure I wasn't missing anything left behind outside of the strainer, and it was free and clear.
 
I contacted a few local HVAC guys, and no one will work on a boat. I tried to explain that it's basically the same process how to troubleshoot any heat pump, but they insisted that as company policy - they don't work on boats. I called 3 places. I called dometic and asked if they had any dealers in the area, and they gave me a number of a guy locally that does HVAC for boats. I'm waiting for a call back.

I'm interested to see what the issue could be.
 
you said you checked the incoming water strainer...what about the air filter that is in front of the fan?.....it should be a very thin piece of mesh that filters the incoming air....it is washable and reusable....is it clean?

cliff
 
CliffA said:
you said you checked the incoming water strainer...what about the air filter that is in front of the fan?.....it should be a very thin piece of mesh that filters the incoming air....it is washable and reusable....is it clean?

cliff
Click to expand...

When troubleshooting, I completely removed the mesh filter from the unit. It wasn't even that dirty, but I washed it off and let it dry.
 
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