Webasto FCF Reverse Cycle Freezing?

[a64pilot]

Originally Posted by transmitterdan

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.

I don’t think they do either, that is usually a air exchange house heat pump thing.
They will go into defrost cycle and kick in the heat strips when they do to keep from blowing freezing air into the house, if a small marine package unit had a defrost cycle, it would of course blow freezing air into the living space as there are no heat strips, trust me, you would notice it.

[a64pilot]

Both my Webasto’s when in hearing mode first start in cooling mode, then after running for 30 sec or so, you hear the whoosh as the reversing valve kicks in and they go to heat, if a valve were sticking it would mess up then.
I’ve only noticed this behavior when first starting it, it doesn’t do it at each compressor cycle, but does when first turned on.

[CapnCrunch]

Originally Posted by TooCoys

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.

In case nobody has suggested this - if you're at a marina, try connecting the city water directly to the input side of your unit and open the water valve all the way. Let it run wide open for at least a day. I have had this same unit for 6 years and the only trouble Ive had with it is once the pump failed and once the coils got caked up with river mud which I resolved with the above method. In both cases, you will get an E6 error code which is "high head pressure" which almost always caused by an insufficiency of exchange water flow. My units (I bough the same unit for my 44' sail boat last year) only frost up when the water temp gets below 40 degrees. Ive always switched over to inductive heat before the marine unit froze up.

[OzePete]

Originally Posted by a64pilot

I don’t think they do either, that is usually a air exchange house heat pump thing.
They will go into defrost cycle and kick in the heat strips when they do to keep from blowing freezing air into the house, if a small marine package unit had a defrost cycle, it would of course blow freezing air into the living space as there are no heat strips, trust me, you would notice it.

Yes, they apparently don't have de-ice protection like what is common on nearly all reverse cycle air cons, but why not?
Even a cheapy split has a de-ice thermostat and there are more reasons why a far more expensive air-con operating in a much more variable environment should have one as standard. Besides they are only a few dollars!
A de-ice device switches off the indoor fan prior to reversing the refrigerant flow using hot gas to defrost, so it doesn't blow freezing air into the living space.

Cheers OzePete

[transmitterdan]

I think this is a <$2K unit which means the parts cost has to be about $250. An extra dollar or two is a lot.

[a64pilot]

Originally Posted by OzePete

A de-ice device switches off the indoor fan prior to reversing the refrigerant flow using hot gas to defrost, so it doesn't blow freezing air into the living space.



Cheers OzePete

Ones I am familiar with do not, the reason is they need the airflow to prevent icing the air handling unit inside of the house, they kick in the “Heat strips” and those rewarm the air, without air flow you merely swap the iced coil.
De-ice mode is of course just the reversing valve operating so that the system runs in cooling mode.
Many if not most are on simple timers and most often deicing isn’t necessary, just the timer runs out. Better ones incorporate a temp sensor and you have to have a frozen coil to go into deice mode.

Boats don’t have a de-ice mode, cause they don’t need one, if there is enough waterflow, it can’t ice.

Remember deice mode is for an air heat exchange unit, and your pulling heat from cold air, air that is often below freezing to begin with, so icing the coil is going to happen.

[Richard Kollmann]

When frost forms on seawater condenser as shown in picture there is a problem in high pressure side of system. Has anyone checked amperage against manufacturers performance chart? And where does frost begin?. Low on refrigerant or reverse cycle valve trouble.

[OzePete]

Originally Posted by a64pilot

Ones I am familiar with do not, the reason is they need the airflow to prevent icing the air handling unit inside of the house, they kick in the “Heat strips” and those rewarm the air, without air flow you merely swap the iced coil.
De-ice mode is of course just the reversing valve operating so that the system runs in cooling mode.
Many if not most are on simple timers and most often deicing isn’t necessary, just the timer runs out. Better ones incorporate a temp sensor and you have to have a frozen coil to go into deice mode.

I think you are confusing defrosting of a refrigerator’s forced draft cooling coil with de-icing of a reverse cycle air con in heat mode. They are similar but different. Defrosting of a forced draft cooling coil is usually timer initiated and time / thermostat terminated. Defrosting of a forced draft cooling coil can be via hot gas, electric heater strips, water etc.
Air con de-ice uses hot gas to de-ice, very rarely heat strips and is initiated and terminated via a de-ice thermostat. A proper de-ice system shuts off the inside air handing fan during de-ice and for a short period after to prevent cool air circulation.


Boats don’t have a de-ice mode, cause they don’t need one, if there is enough waterflow, it can’t ice. Well this one and others quoted certainly need one!

Remember deice mode is for an air heat exchange unit, and your pulling heat from cold air, air that is often below freezing to begin with, so icing the coil is going to happen.

No, de-ice is not just an air heat exchange issue! The system works similarly regardless of the heat source and the variation of water temperature (like air) temperature should make de-ice protection a no-brainer!
Another reason why ALL reverse cycle systems should have a de-ice device, is to protect the compressor from ‘liquid slugging’ which can occur once there is insufficient heat to boil off all refrigerant and refrigerant is able to return to a running compressor as a liquid. Not having a De-ice on these systems is not good at least!

The problem indicated by the OP picture is simple: There is insufficient heat to maintain that exchangers temperature to below water freeze point... simple. Either the water flow is insufficient or restricted.

The OP’s problem has absolutely nothing to do with, nor is caused by, the condenser refrigerant pressure or the reversing valve sticking or being low on refrigerant or amperage!
This system as shown would present with both high side and low side pressures abnormally low and amperage low also (low due to these low pressures), but these factors are all SYMPTOMS of the problem, nothing to do with the cause which as stated, is simply a lack of heat where evaporation is trying to occur..

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems

[Richard Kollmann]

Pete, what would you say if amperage draw is 20% to 30% below normal on ambient air chart for that model unit.

[OzePete]

Originally Posted by Richard Kollmann

Pete, what would you say if amperage draw is 20% to 30% below normal on ambient air chart for that model unit.

Richard, a power consumption rate 20 to 30% (or more) below normal is about what I would expect that iced up system to be running at. As you know the ice covering the evaporator would reduce the suction pressure considerably and that reduced suction pressure would therefore reduce the high side pressure relatively. A system operating with abnormally low pressures will have less compressor load and therefore lower power consumption rate.
All above pressure / consumption issues are symptoms of a frozen over evaporator, not the cause.

Cheers OzePete

[a64pilot]

Pete, I guess we will disagree again.
Just as one example you don’t prevent slugging with a deice system, you prevent slugging with a compressor heater.

So someone please show me a boat heat pump that regulatory uses the reversing valve to kick the system into the cooling mode to de-ice the water heat exchanger?
I’m sure there are some, just I’ve not seen one, but I don’t “Do” Boat HVAC systems either, I just piddle with refrigerant systems as a hobby of sorts

[OzePete]

Originally Posted by a64pilot

Pete, I guess we will disagree again.
Just as one example you don’t prevent slugging with a deice system, you prevent slugging with a compressor heater.

Sorry mate, but we disagree yet again, but that's healthy!!
Compressor sump heaters are often used to prevent liquid slugging. But, these heaters are to prevent migrating liquid build up in the compressor sump during off cycles, not to prevent liquid slugging due to un-evaporated liquid entering the compressor while running.

You can prevent liquid slugging of any R?C air con when operating in heat mode, with a de-ice device. Millions of R/C air-cons, air or water cooled prove that! Such a device on any air con, if set correctly, will prevent ice build up to the extent that only mostly evaporated refrigerant, not liquid refrigerant, would be entering the compressor .

So someone please show me a boat heat pump that regulatory uses the reversing valve to kick the system into the cooling mode to de-ice the water heat exchanger?

The OP has has a system that should have a de-ice set up, my point being that even the millions of cheep R/C air cons from Walmart or where ever have de-ice protection so why not these far more expensive systems?
I’m sure there are some, just I’ve not seen one, but I don’t “Do” Boat HVAC systems either, I just piddle with refrigerant systems as a hobby of sorts

BTW, you stated "Just one example" so what else do you want to disagree with!

Cheers OzePete..

[a64pilot]

I’d rather not argue, that was enough

[Richard Kollmann]

Originally Posted by a64pilot

I’d rather not argue, that was enough

Cheers to the Moderator

[DeepFrz]

Has anyone noticed that many posts ago the OP stated his problem had been solved by setting the control to AUTO?