A/C Freezing

[Lee Hadjiosif]

My marine A/C after working great for over 5 years, is now starting to freeze up after working for a while. The filter, air ducts, etc are clear and air is flowing fine when the coils are not frozen. I understand that I may be low on refrigerant, but I also have a "freeze sensor" which is clamped on to the pipe near the coil (which also freezes) and is supposed to shut off the compressor when frozen, but it doesn't. If I turn off the compressor manually until the unit is defrosted and then back on again, it can work fine for a few hours but it will happen again. So, my theory (and question) is that if the freeze sensor does not shut off the compressor, it must be defective. On the other hand if the evaporator didn't freeze, I would never notice a bad freeze sensor. It's like the chichen or the egg! I would like to ask for opinions if I should first replace the sensor (about $90) and see what happens, or first have the freon checked/charged and leave the sensor alone. Anyone else with this problem? Thanks.
Lee
S/V Calaloo

 

[C Jones]

Lee, only two things will make any a/c system freeze up. Thats lack of refirgerant (low on freon) or lack of air flow thru the evaporater. It may be low on freon or your evap. coil may be dirty.
Your blower may be turning slower or stopping for what ever reason. Your evap coil could be dirty or plugged up and look ok on the surface. Good luck Charles

 

[Lee Hadjiosif]

Charles, Thanks for the quick reply. I was wondering about the purpose of the freeze control sensor.

 

[Allan12210]

Air con problems can be tricky. If the compressor isn't cycling properly then the evaporator will freeze up (i.e., running all the time). There is an expansion orifice leading into the evaporator. If it is the temperature controlled type, then when they get sticky, they can allow too much coolant into the evaporator leading to freezing. If the coolant level is low it is best to figure out where the leak is before refilling it. Basically the bottom liine is it might cost more to start replacing parts (like I did) than to just have a refrigeration technician do an assesment and repair it. I know, I like to do as much as possible myself, but AC is a tricky one and it took hooking up the gauges to the high and low pressure side of the compressor and correctly interpreting the results. My problem became too much oil in the system after I replaced the condenser (it did have a hole in it), then the compressor and finally the expansion valve. I would have it recharged...it wouldn't cool, have it evacuated, change something else and finally admitted defeat and had the AC guys flush it completely with the correct solvent and restarted with the correct amoun of oil and refrigerant to finally get it up and working the way it should.

Good luck.

Allan

 

[Cliff E]

do you know where it starts to freeze first. like lee said, low freon or low air flow probably the problem. I think if it is right it should be able to run 24-7

 

[Cliff E]

sorry like C Jones said, and I have bad luck with freeze sensors. it could also be a restiction in the freon flow, kinked line or clogged exp valve.

 

[kloudie1]

I agree with previous posters.. Low freon is most probable cause.. Is sounds like a very slow leak so it will be almost impossible to find without a detector.. The service guy is expensive, but unless you have the specialized tools and knowledge, probably the least expensive path... Lots of times, the freeze sensors are mounted at the most downstream point in the evaporator.. the last place to freeze if the freon is low.. so it may be operable but not sensing what it needs to.. You can test it by making a glass of ice water and putting a couple of tablespoons of salt in it and waiting a 3-4 minutes.. Then put the sensor in the icy brine with the compressor running and see if it trips the compressor..

 

[Benny17441]

Either low Freon or reduced or obstructed airflow.