A/C freezing up...

I have an 86 Sea Ray 270 Sundancer. It has a Marine Aire 12,000 btu unit with the two knob thermostat. It freezes up when it runs, mainly at night, or for a lengthy time. For some reason, it doesnt cycle off, it constantly runs. If I turn the thermostat up, the compressor kicks off, and the fan runs but it will not cycle back on...Filter is clean, coils are clean, and freon is good.....Not sure what else it could be.....any ideas?
Oh, and for some reason, there is only one exit for the duct, and it is on the port side, through the upper cabinet where the stereo is....would this have anything to do with it??

Either a lack of supply or return air flow will cause your condition. My 12000 BTU unit has one large, one medium, and one small air supply ducts along with four air return grates.

Regarding your problem with the unit's compressor not restarting after you turn the thermostat up, does your system switch from A/C to Heat as the ambient temps change? Not sure about the manual dial systems (mine is digital). If it's on A/C only the compressor will not come on by increasing the "set" temp.

PlayTime said:

I have an 86 Sea Ray 270 Sundancer. It has a Marine Aire 12,000 btu unit with the two knob thermostat. It freezes up when it runs, mainly at night, or for a lengthy time. For some reason, it doesnt cycle off, it constantly runs. If I turn the thermostat up, the compressor kicks off, and the fan runs but it will not cycle back on...Filter is clean, coils are clean, and freon is good.....Not sure what else it could be.....any ideas?
Oh, and for some reason, there is only one exit for the duct, and it is on the port side, through the upper cabinet where the stereo is....would this have anything to do with it??

Click to expand...

Is your unit AC only or is it a reverse cycle unit that will also give you heat? If all of your grilles are clean, etc. I would then suspect air flow across the coil is insufficient. Can you increase the fan speed? I am not familiar with a two knob thermostat. Both of mine are 3 knobbers. What do each of your 2 knobs do?

~Ken

electricaldoctor said:

Is your unit AC only or is it a reverse cycle unit that will also give you heat? If all of your grilles are clean, etc. I would then suspect air flow across the coil is insufficient. Can you increase the fan speed? I am not familiar with a two knob thermostat. Both of mine are 3 knobbers. What do each of your 2 knobs do?

~Ken

Click to expand...

I am not sure if I can increase the fan speed or not...trying to find a manual on it...as far as the knobs, the top one says off, fan, and cool...the bottom one is temperature....I think it is a straight cool system. I am thinking of extending the duct to the aft cabin as well somehow. It only has one large duct for output..no vents...dont know why....is it possible that because of the cold air, it sucks it back into the return do to lack of dispertion? If that makes sense????

Jimmy Buoy said:

Either a lack of supply or return air flow will cause your condition. My 12000 BTU unit has one large, one medium, and one small air supply ducts along with four air return grates.

Regarding your problem with the unit's compressor not restarting after you turn the thermostat up, does your system switch from A/C to Heat as the ambient temps change? Not sure about the manual dial systems (mine is digital). If it's on A/C only the compressor will not come on by increasing the "set" temp.

Click to expand...

I would think, as a regular a/c system, the compressor would shut off once it reaches its operating temp, then kick back on when it needs to cool again....

AC units freeze up for one of three reasons: too low of base temp setting, restricted air flow or low refrigerant.

msd58 said:

AC units freeze up for one of three reasons: too low of base temp setting, restricted air flow or low refrigerant.

Click to expand...

:thumbsup: +1 Yep, check all of these and I bet you'll find your issue.

msd58 said:

AC units freeze up for one of three reasons: too low of base temp setting, restricted air flow or low refrigerant.

Click to expand...

Air flow not restricted, freon is good. Now, what is too low of a base temperature setting? I have to turn it all the way cold for it to kick on, or else the compressor wont turn on....

PlayTime said:

Air flow not restricted, freon is good. Now, what is too low of a base temperature setting? I have to turn it all the way cold for it to kick on, or else the compressor wont turn on....

Click to expand...

Perhaps it is time to retire that old 2 knobber control or is the sensor properly located in the air stream or is it located off to the side where it will not properly sense the room temperature properly?

Is it actually freezin up or just shutting down from a low pressure sensor? Do you actually see ice? If your cooling water volume is too low, the system will shut off from high pressure on the condenser side.

I thought about replacing the thermostat with a more updated one. It is located right next to the unit, where the return air is. as far as ice, yep, definitely ice! If I dont keep an eye on it, it will turn into a solid block! It doesnt do it right away, it takes a while. During the daytime it takes longer to start to freeze, a few hours anyway. At night, it happens within a couple hours...

Just don't think there is enough Freon in the system. The only way it will Freez up is if the temp(pressure) in the sytem gets below 32 degrees. the only way this can happen is if the freon volume is too low. Need to check the charge. Don't think the charge is high enough.

"freon is good."

How do you know this?

I'm late entering this thread. Are you still having a problem with it?

everybody's between close to dead on. here are a few details that may help clear up the data you have received.
the two knob systems are cool only. there is no low pressure sensor on the mechanical style otherwise known as two or three knob controls. the fan speed controls and thermostat are made by industrial makers and the boat air conditioner people buy them for use therein. they turn the fan speed control to bare minimum in order to keep people from turning the fans down too low and icing the machines. if you look at the back of the fan speed switch you will see a little warning decal placed over the tiny hole in the switch body that can be used to adjust fan control parameters.
too slow a fan speed and you will ice up for sure.
turn your unit off and hold your ear to the thermostat. slowly turn it from extreme to extreme. you will hear a tiny click inside it when it reaches the "turn on point". take note of the range of travel you must turn the thermostat in order to hear the click for on and off. there is an adjustment for that range as well. if you hear no click the t-stat is bad. the sense bulb must be located in the return air stream just in front of the evaporator. if its not there the unit will not respond as it should to warming and cooling in the conditioned spaces. so...check the t-stat settings and check it for even working, if its run time is too long the unit will freeze. make sure that sense bulb is where it needs to be. if you want digital Cruisair has great conversion kits out. i have them on my home airs. in fact, i have cruise air marine units cooling my house using the swimming pool as a water source. real small, super efficient and fun to mess with. point is to say you can fit the digitals on your two knob machine.