Webasto FCF Reverse Cycle Freezing?

[OS2Dude]

Have you checked the manual? Are you getting an error code? From our 24K FCF:

Coil is iced

Thermostat set point is too low Raise set point.

Improper air flow Remove any obstructions in return air stream. Clean return air filter and grille. Check for crushed or restricted ducting, ducting must be as straight, smooth and taut as possible.

Supply air is short-cycling, Redirect supply air so that is not blowing into the return air stream. Seal any air leaks on duct.

Seawater temperature is below 40oF Shut down system to prevent damage to condenser.

Allow coil to defrost (see below).

Humidity level too high. Close hatches and doors.
When all else fails. Switch air conditioner to heat until ice melts or use hair dryer to melt.

[TooCoys]

Here is the current water flow. I just turned it on after being off since yesterday.

https://www.youtube.com/watch?v=obFHAR3iOMo

[Sailmonkey]

That doesn’t look bad.

You said the tech descaled the condenser?

How long did the coil sit with clr or ridlyme, etc... it it?

[Cadence]

I'd guess you have a reverse cycle valve hanging up or a control problem to the solenoid valve. If it is icing up I'm afraid you through that service charge away.

[transmitterdan]

Originally Posted by TooCoys

Here is the current water flow. I just turned it on after being off since yesterday.

Doesn’t look like enough water flow to me. You are not running in cool mode but in heat mode. It needs lots more water flow for heat mode than cool mode. The colder the sea water the more flow you need to prevent freezing because delta T is reduced. I would find a different technician that knows how heat pumps work.

[TooCoys]

Originally Posted by Cadence

I'd guess you have a reverse cycle valve hanging up or a control problem to the solenoid valve. If it is icing up I'm afraid you through that service charge away.

Would that cause it to never shut down?

The condenser will kick off and the water pump will stop when temperature is reached but the fan NEVER kicks off.

[a64pilot]

I know it’s a Pain, but time how long it takes to fill a 5 gl bucket.
Of course that will tell you flow.
500 GPH is I believe a gallon ever 8.3 sec.
That is a LOT of water

[a64pilot]

Originally Posted by Cadence

I'd guess you have a reverse cycle valve hanging up or a control problem to the solenoid valve. If it is icing up I'm afraid you through that service charge away.

Can’t be, the only thing I that could ice it up is inadequate heat exchange through the evaporator, which is of course water heated, airflow doesn’t enter into it either.

We are talking about the inside of the coil freezing up and preventing water flow, and not just ice on the outside, right?

[Shrew]

Originally Posted by TooCoys

You haven't said anything that hasn't been said by 100 other people, so we checked all that. Unfortunately we're still coming up with nothing.

Technically, he is the first person in this thread to mention descaling. You didn't mention the technician descaled the system.

The pump has a 500 GPH pump is its max capacity. A restriction will significantly lower the volume regardless of the capacity of the pump.

[transmitterdan]

Originally Posted by a64pilot

I know it’s a Pain, but time how long it takes to fill a 5 gl bucket.
Of course that will tell you flow.
500 GPH is I believe a gallon ever 8.3 sec.
That is a LOT of water

Every 7.2 seconds to be exact (3600/500). And that video doesn't look anything close to a gallon every 7.2 seconds. I don't think 500 GPH should be needed. But certainly it takes significant flow to put enough heat into the evaporator coil to prevent freezing. If the water temp is 60F that's 15.5C. So the water temp can only drop 15.5C before it freezes. In summer time when in cooling mode the sea water temp may be 80F or 27C. In that case, the outlet water temp can be 50C or more which is 23C delta and the A/C will still work (albeit it not too efficiently). But in cool mode that much delta-T will freeze the thing pretty quick. And copper water loops don't respond well to freezing.

[transmitterdan]

Originally Posted by TooCoys

Would that cause it to never shut down?

The condenser will kick off and the water pump will stop when temperature is reached but the fan NEVER kicks off.

All of the all-in-one A/C units that I have ever used, the blower runs 100% of the time. Only the more sophisticated systems have blower thermostats. In the all-in-one units the thermostat just starts and stops the compressor + water pump. So yes, the fan runs all the time which is normal for most systems like yours.

[Sailmonkey]

Originally Posted by TooCoys

Would that cause it to never shut down?



The condenser will kick off and the water pump will stop when temperature is reached but the fan NEVER kicks off.

The fan never turns off, the temperature sensor is in front of the evaporator, so it must move air to sense the temperature.

I’m betting you’ve got a combination of scaly crud from our delightful water and a flow restriction adding up.

[OzePete]

Originally Posted by OzePete

This thing is trying to absorb 16K BTUs /Hr of heat from what appears to be a relatively small heat exchanger. It would require full water flow and more importantly a very clean heat exchange area, internally within the area where heat exchange is intended. For example, if the interior of the exchanger tubing is coated so as to restrict heat transfer, you may have a good water flow but it is 'insulated' from collecting the correct / engineered amount of heat. This would cause the condenser to perform poorly, gradually allowing its external surface to lower below 32F and build ice as a consequence.

Suggest you have the exchanger properly cleaned, water pump flow rates tested and enquire if the system has an operating de-ice device.

It is not short of gas.

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems

Repeat..... specially since viewing that very low water flow.

[.Paul.]

Originally Posted by TooCoys

Would that cause it to never shut down?

The condenser will kick off and the water pump will stop when temperature is reached but the fan NEVER kicks off.

I had a similar problem. With factory settings both the compressor and water pump would stop when the room temperature reached the setpoint.

The fix was to change the control settings to only stop the compressor when the setpoint is reached. The pump runs continuously while the thermostat cycles the compressor. The pump needs to run for a few minutes after the compressor stops in order to warm the heat exchanger. If they both stop at once, the cold metal in the heat exchanger can freeze the water.

Paul

[TooCoys]

Ok. Tomorrow I’m going to get a 5g bucket, some hose, and some barnacle buster or something and run a cycle to descale the coils and also measure the output.. I’ll report my findings. Although I fully believe they will be within specs.