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Old 05-12-2018, 14:50   #31
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Re: Webasto FCF Reverse Cycle Freezing?

I'm in the process of installing my Webasto FCF Platinum 12K btu unit purchased last month from Defender. I did not get the icing up as you are experiencing in heat mode, but rather the unit would short cycle with high temp coming from the duct. Talking to Webasto they told me to check the water flow coming out. I measured 4 gpm which I was told was too low even thought the installation manual said differently. I have a 1000gph pump. I then redid my hoses and increased the diameter and was able to get 5gpm. I then ran the unit again with the increased water flow and noticed the same thing. I then disconnected the ducts and ran again and everything worked fine. I was told that I needed more outlet and supply air flow so that is what I'm been doing for the past 2 weeks. When I bought the unit I thought that the 5 inch blower could go to a wye with two 4 inch ducts. Wrong.....the 5 inch blower is to go to two 5 inch ducts. Also I'm increasing the area of the supply air. Drilling those 5 inch holes in the bulkhead was a dreaded task, but it went easier than I expected. My guess is that your water flowrate is too low. Good Luck
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Old 05-12-2018, 15:03   #32
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Re: Webasto FCF Reverse Cycle Freezing?

minor point..
500gph/60minutes - 8.33 gallons per minute not per second..


are your water lines without 90 degree bends? and/or anything that might
slow the flow down?


its the actual rate not the pump rating that matters
google the pump specs..you might find that an 10psi the flow rate is 100gph..instead of 500gph...


-dkenny64
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Old 05-12-2018, 17:39   #33
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Re: Webasto FCF Reverse Cycle Freezing?

Quote:
Originally Posted by dkenny64 View Post
minor point..
500gph/60minutes - 8.33 gallons per minute not per second..
Yes, you are right. And a flow rate of 8.333 gallons per minute will fill a 1 gallon container in 7.2 seconds.
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Old 05-12-2018, 20:32   #34
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Re: Webasto FCF Reverse Cycle Freezing?

Thinking more about your problem with freezing, I had just the opposite reaction from low coolant flow when in heat mode. The webasto folks said that below 43 degree water temp there is not enough heat to work the heat pump however if you throttle that water flow down you can get some heat from that of the compressor. Never did say how low a water temp that would work. On my 12K unit, the cooling mode is rated for 12K while in the heat mode its rating is 13K due to that heat from the compressor. Your 16K unit does not show any difference in the specs. ??
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Old 05-12-2018, 21:18   #35
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Re: Webasto FCF Reverse Cycle Freezing?

Think about it this way. The evaporator coil is inside the water coil. The evaporator coil is really cold. Now if you run water really fast over the evaporator its temperature cannot get as cold as the evaporator coil. The slower you run the water the colder the water will get before it escapes the coil.

So the faster you run the water the more heat can be extracted from it before the water cools too much and freezes. The exact opposite of what you might think. But it makes sense if you consider that the water has heat. The more water you put in the more heat you can get out of it.
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Old 05-12-2018, 21:22   #36
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Re: Webasto FCF Reverse Cycle Freezing?

Reverse cycle air con systems of all varieties should and usually do have a de-icing device. This is simply a thermostat that monitors the condenser temperature so that when in heating mode, (and the condenser becomes the evaporator) if the temperature lowers to where it causes frost restricting air flow or in this case ice restricting water flow, the indoor air distribution fan is switched off and the system refrigerant flow is reversed from heating to cooling for several minutes. This sends a rush of heat to clear the evaporator, then once clear this thermostat reverts the system back to normal operation.

Now I have no experience with this brand but it doesn't appear to have this otherwise common protection.

This de-ice control could be added via a digital thermostat and double pole relay and some wiring.

The digital controller's thermistor (sensor) would need to be located in the most sensitive spot where frost / ice build up occurs. This thermostat would simply supply/ switch the relay. The relay would do nothing until the thermostat switches at say +35F (2C) when it would be activated. At that time the relay would disconnect power supply to the indoor fan and switch the reversing valve. This would cause the indoor fan to stop and the system reversing valve to reverse the refrigerant flow causing defrost / de-icing. Once clear of frost / ice the thermostat would sense the temperature rise and revert back to normal status.

Seems complicated but really quite simple, although a bit a tweaking the thermostats cut in and cut out points would be needed. But once done there would be no more frost over or ice up.

Regardless of having a de-ice control or not, the flow of heat, in this case via water, is critical.

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems
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Old 06-12-2018, 03:59   #37
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Webasto FCF Reverse Cycle Freezing?

Pete,

I don't think any of these small self contained A/C units have automatic defrost function. They rely on two things typically. The fan runs all the time so that helps. And they have a high and sometimes low coolant pressure switch. But I agree with you that the water has to flow in sufficient volume to put enough heat into the evaporator coil. There is no other place to get the heat.

We have a 16K BTU reverse cycle unit too. It does not freeze even though our water temps dip down to 45F. But the water stream is a lot stronger than the video above. We have no elbows as the system uses a single rubber hose from the pump to the heat exchanger so all the turns are nice and smooth. We have a March LC-3CP pump that I think is rated for 500GPH but we only get about half that flow rate.
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Old 06-12-2018, 08:18   #38
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Re: Webasto FCF Reverse Cycle Freezing?

Well now I’m wondering if it was operator error. I got the manual out last night and read step by step how to set the heat cycle. It’s been running in auto fan and auto heat since early yesterday evening at 68 degrees and it’s ran all night without any frost in the coils.
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Old 06-12-2018, 09:00   #39
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Re: Webasto FCF Reverse Cycle Freezing?

Webasto service said that it’s probably a partial opening of the reverse valve. They suggested cycling heat and cook a few times to make sure the valve is fully lubricated.
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Old 06-12-2018, 17:29   #40
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Re: Webasto FCF Reverse Cycle Freezing?

Water flow looks low to me but I am no expert.
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Old 06-12-2018, 18:10   #41
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Re: Webasto FCF Reverse Cycle Freezing?

I’m thinking it’s a reverse valve not opening, as webasto said. It’s been on auto fan and auto mode since yesterday, it’s ran all day,, and the coils are not frosted, nothing feels overheated, and it seems to run fine.
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Old 06-12-2018, 19:32   #42
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Re: Webasto FCF Reverse Cycle Freezing?

Just FYI, on Webasto FCF units if the power is on the fan is running. Even if they are not actively cooling or heating the fan is running.

Also, their thermostats are terrible, routinely over cooling or over warming by as much as 4 degrees from setpoint. And they are not supplied with service valves. And their remote is a joke. And their control board is vintage 1980s tech and responds to control inputs in minutes not seconds.

I've owned 2 relatively new units on different boats, never again.
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Old 07-12-2018, 08:35   #43
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Re: Webasto FCF Reverse Cycle Freezing?

Flagship marine controls are even older using contactors and relays that operate immediately. They also don't burn out when voltage is low. They use a non proprietary thermostat and are now offering the ability to use any one of the new WiFi thermostats as a standard configuration.
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Old 10-12-2018, 09:43   #44
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Re: Webasto FCF Reverse Cycle Freezing?

I have the same 16k unit as you...I bought it complete with the installation package. I have had no issues with mine but I do think my water flow makes yours look like a trickle.
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Old 10-12-2018, 16:19   #45
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Re: Webasto FCF Reverse Cycle Freezing?

based on what was happening on my old cruise air unit..
I don't think its the reversing valve sticking..
if the reversing valve sticks the compressor pressurizes both side...if the compressor stops and tries to restart its starting against full head pressure. it'll trip the breaker...


this unit doesn't have 80's tech electronics. sorry..my old cruise air has that..its all mechanical.. BoatandBeach sorry you don't like them... for the set point..it would help if the fan ran all the time...I've not figured out how to set this yet..


-dkenny64
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