CruiseAir limited heat function

One of the CruiseAir units on the boat will only run at low fan speed in the "heat" mode. It cools fine at all fan speeds. When the heat mode is initially engaged, it initially goes to high fan speed (as expected), then the control panel flashes a momentary "pressure" alert (can't recall if it's "hi" or "lo"). and then the fan speed drops to minimum, where it does heat OK. It just won't heat at fan speeds above the minimum setting. Any clues? Thanks.

Well, it depends on whether it flashes high or low as to what is wrong.

David

OK....whatmight be wrong if it flashes HI....and what might be wrong if it flashes LO? (I think it's LO if memory serves me...it doesn't so much these days...) And why would it still blow ice cold in the cooling mode and shift to low fan speed when in heat mode in either case? (Unfortunately the boat is currently in heated winter storage up on the Great Lakes, and I'm at the house in Texas...just trying to get the jump on Spring trouble shooting/repair). Thanks

Low pressure at high fan speed makes me think that either the system isn't getting enough water flow or the water is too cold. Or both. So when pulling enough heat out of the condenser (air side when in heat mode) the pressure drops below the threshold. I'd expect possible high pressure faults in A/C mode when the water is hot in late summer if it's a water flow problem.

Compare the water out FLOW. One line may be plugged up a bit.

Check the inlet hose too. Seems, once a year my inlet hose does not allow enough flow due to sea creatures build up.

Thanks for the vectors, gents. I only use the heat in the aft cabin in the early Spring and the Lake Michigan water temperature is indeed pretty cold...mid-40's-50s. That said, the big unit up in the salon works pretty well in the same conditions (shared cooling water pump). Anyway, food for thought. Much appreciated.

"(shared cooling water pump)."

When used as a heat pump the system moves heat from the sea water into the boat. .

Perhaps the local water is so cool that after heat has been removed the next unit in line cuts back to not freeze the sea water?

FF said:

"(shared cooling water pump)."

When used as a heat pump the system moves heat from the sea water into the boat. .

Perhaps the local water is so cool that after heat has been removed the next unit in line cuts back to not freeze the sea water?

Click to expand...

There is a couple of ways to hook up the sea water.
1. each unit has its own SW pump
2. one pump and 2 units share it.... Like my AT34, 2 units and a high volume SW water pump. Each unit has their own discharge.
I have not heard of a system where the SW feeds one A/C and the outlet feeds the second unit. In my feeble mind, I would think that is very inefficient.
I personally would like one SW pump for each unit but, the AT34 has one SW pump and 2 units. I guess I could reengineer the system but, the current configuration works fine until the hose from the hull valve to the SW strainer gets plugged up with sea creatures then , time to change the hose.

Our boat is set up with a "splitter "between the cooling water pump and the two units. So the AC units are not in series. Two dedicated raw water pumps would be better, but it works fine when they're operating in the cooling mode. In actual practice, I use a small electric wall heater in the aft cabin when it's cold at night...quieter, less drafty air flow, and probably uses less power. Would still like to understand what's happening with that aft AC, though.

How far aft?
The outflow of the water, it is about the same as the fwd unit?
When was the last time you had the plants descaled?
Check the SW hose from the pump to the aft AC.

FF said:

"(shared cooling water pump)."

When used as a heat pump the system moves heat from the sea water into the boat. .

Perhaps the local water is so cool that after heat has been removed the next unit in line cuts back to not freeze the sea water?

Click to expand...

Good point. I know when the water is about 42f, my does not put out any heat.

What is the temp of the water?

Maybe try some Barnacle Buster in the cooling hoses. We put some in ours last year and let it sit for 6 hours I believe. Then turn on the system and let it flush out.

Comodave said:

Maybe try some Barnacle Buster in the cooling hoses. We put some in ours last year and let it sit for 6 hours I believe. Then turn on the system and let it flush out.

Click to expand...

Based upon my experience with a 2ftX1inch hose from the hull valve to the sea strainer, it does take far less time to change out the hose plus, a new hose eliminates ready made places for the sea creatures to cling

But replacing the hose won’t clean out the tubing in the A/C which could have buildup in them.

Comodave said:

But replacing the hose won’t clean out the tubing in the A/C which could have buildup in them.

Click to expand...

Very true but descaling will clean out the coils.

That is what BB does.

The AC system was installed while the boat was on Lake Travis in 2006. Then the boat was moved to the Great Lakes and only used for a few month each year. No salt water ops at all. I back flushed it four or five years ago, but not with a cleaner liquid. The rear unit is situated on the same bulkhead (opposite side) as the forward unit and a few feet lower in the hull (on the floor of a closet in the aft cabin). Water temp is typically in the 50 degree range, but it seems to malfunction at any temperature....although I've not tried it on a 90 degree day with water temp in the 70's. Top unit works fine...as expected a little slow to heat up when the water is cold, but it always works without throwing a fault signal.

Given the way this thing immediately blinks a momentary pressure signal, and then immediately shifts the fan down to low speed the exact same way every time regardless of water temperature, I'm inclined to think it's a switching malfunction or a genuine pressure issue. It's just odd that it works fine in the cooling mode.

Anyway, thanks everyone for the tips. I'll look closely at that fault warning when I splash the boat in the Spring and make a point of backflushing/cleaning the lines and the unit.