CruisAir

[Paul]

I have a CruisAir 12,000 BTU air conditioning unit with reverse heat and a seperate blow thru evaporator. This unit works perfectly when running the A/C however when using the heat, the compressor tends to kick off during it's cycle.

To better explain this, when I set the thermostat (three knob) to warm up the boat in the evening it quickly starts blowing heat, lots of heat. Then before the thermostat reaches the set temperature, the compressor will kick off as if a seperate overload in the compressor itself is controling the cycle. It only stays off for about 10 - 15 seconds then comes right back on. This repeats three to four times until the cabin gets up to temperature and the thermostat shuts it down.

It almost seems as though the unit makes more heat than the evaporator can deal with. The water system consists of a strainer and a liquid cooled March pump and is working perfectly.

Any thoughts???

[Big D]

Paul, I'm assuming this is a recent new problem and that nothing has been changed or done recently that would affect operation. I suspect you've already checked the evaporator fins and filter to ensure they are dust free and that nothing is blocking air flow. Are you sure you have full water flow exiting the unit? Does the fan sound like it's turning slower than before? Do you see frost build-up on any lines? If you have a lazer temp gun, at what temp taken at the t-stat probe does the unit start to cycle on and off?

[Paul]

Big D,

I purchased the unit used and installed it a few years ago. Its done this from day 1. Air flows freely thru the evaporator and the problem still exists weather the fan is on hi or low. The water flows freely as well.

I don't know about frost on the lines however. The next time I go to the boat I'll check and also take some temp readings.

Thanks,

[Big D]

Did you install the unit? Where did you place the t-stat probe? Gather all the info that you can, temps, model, serial number etc. then call Northland in Keswick Ontario.

http://www.norsupco.com/

[reelfishin]

You are saying there are two units the condernsor and the evaporator. Since it is a heat pump there should be two TXV.s and two Check valves. I believe you have a problem with a check valve installed wrong or a txv not working correctly. To check the TXV you will see it frosting if it is not working correctly. You may have your unit miswired too. A txv may not be wired into a circuit at the evaporator. Just my thoughts. Would like to know what you find. That is if I am reading your question right.

[prowlersfish]

reelfishin you still across the pond ? haven't see you or the boat , But I haven't been around as much my self .

[reelfishin]

Yep we still are there. We went offshore last weekend and got a 62 lb tuna. Should be going again in about two weeks. It is a 76 mile trip and we were running close on fuel. Will know how close when we fill up again.
Not sold on that hydrogen system. It is not big enough and I think designed wrong but I am not an expert. It would probably help if the tank was bigger. I might try and do something about that when we pull out next year to paint the bottom.
I now have a small Mckee Craft 16 foot classic (skiff) that I am fixing up for fishing. I think I can have a lot of fun on it.

[prowlersfish]

do you mean 76 miles each way ?

[reelfishin]

yep, that is what my son said. It was a 3.5 hour to 4 hour trip going out and the same coming back. Total about 7.7 to 8 hour cruising plus the trolling we do while we are out there. We cruise at about 20 knots.

[Paul]

Reel Fishin,

I didn't get the chance to run the heat this past weekend to check for frost or temperatures. This unit is two seperate pieces. One with the compressor, heat exchanger, electrical, etc, and fittings where the tubes for the evaporator to hook up. The second piece is the evaporator with a fan mounted on it which can be mounted anywhere in the boat. This unit works perfectly while cooling the cabin but seems to intermitently kick off some type of thermal or electrical protection in the compressor itself when used for heat.

Also, can you please explain what TXVs are? I want to make sure that I'm inspecting the correct pieces.

Thanks,

[reelfishin]

OK, I see what you said about producing to much heat for the evaporator to handle. Could be you have a air flow problem. Check your filter and coil. Make sure they are clean.
A TXV controls the freon that enters the evaporator in the cooling mode. It will have liquid freon coming to the txv and it will let only so much go to the evaporator. The liquid quickly expands or evaporates to a gas and causes cooling the gas which is now cold goes to the condenser or outdoor unit where the compressor compresses the gas( makes it hot) and sends it to the outdoor coil where the compressed gas gives off heat and changes back to a liquid and heads to the TXV and the cycle starts over again.
Now a heat pump uses two txv.s and two check valves to operate heating and cooling. A TXV is also called a Expansion Valve.

[larryeddington]

TXV stands for Thermostatic Expansion Valve and its actions have been described correctly. I do not know about Cruisaire but my reverse cycling HVAC does not use TXV's but uses fixed capillary tubes. you might also see fixed orifices used for metering some times. At least outside the marine industry and these small systems are no different other than they use water for the heat exchanger medium instead of air.

[reelfishin]

Yes thanks for adding that capilliary tubes or orfices are sometimes used. Probably what he has is a capilliary tube. One thing we have not mentioned is the 3 way valve. If it is only going part way and not all the way over it would cause the unit to not heat very well. He should hear a Shooooosh when it changes.

[larryeddington]

The reversing valve could be a problem, however they are pretty dependable. A place to look is the relay that controls the reversing valve, it is highly possible the relay is not working or the control thermostat is not sending a signal to reverse.

Years of working in HVAC has taght me that the first place to look is the simplest, which would be the relay or the thermostat that sends the signel. The best way to find out is to first understand the control circuit, then bypass each component to see if it works manually. If it does you have the offending part.

Larry

[Paul]

Thanks for all of the replies gents. Havn't had much time to spend down at the marina lately but I'm hoping to this weekend. Then I migh be able to isolate the problem.