A/C question (again)-gctid360889

[Guest]

Im burning these forums up and you guys and gals are probably tired of my dumb questions, but here comes another one:

My 2000 ciera 2855 (new body style) is equipped with factoy a/c. The air works perfectly and cools the cabin to 65 degrees in about 20 minutes and then i noticed the air coming out of the vents slows considerably. The air coming out is still cold, but the volume of air is reduced considerably. Is this normal? My question is, does my boat have a thermostat that regulates the airflow to control the temperature? I was under the assumption that the temperature knob was to control the temperature of the air coming out of the vent, not used like a thermostat. Does that make sense? Is there a problem with my fan/blower? Or is it normal for it to cut back on air flow as the cabin cools down?

[JimMc]

In all likelyhood your AC unit is icing up. Try running it again until it slows and check the coils for icing.

If it is icing check the filter to be sure it is clean and not restricting air flow.

My AC unit has a defrost cycle which I have set to run routinely which clears any icing.

I am not an AC guru but I know in past discussions there were concerns that this icing could be caused a lack of refrigerant.

-------

I would be suprised if your thermostat and AC unit could control output air temperature. Typically thermostats control the room or cabin temperature.

[simo]

The temperature knob is indeed a thermostat. After running the AC for a while, turn the knob to 'warmer' just until the compressor turns off. Your fan will continue to run and in a little while as the cabin temp creeps up, the compressor will kick back on. This off/on cycling will prevent excessive icing. If the unit doesn't cycle, then there's a problem with the thermostat.

[Guest]

You are freezing the unit up Cool it down in smaller increments. Check ur air filter, maybe you need more air.

[msd58]

RMSLLC wrote:
Im burning these forums up and you guys and gals are probably tired of my dumb questions, but here comes another one:

My 2000 ciera 2855 (new body style) is equipped with factoy a/c. The air works perfectly and cools the cabin to 65 degrees in about 20 minutes and then i noticed the air coming out of the vents slows considerably. The air coming out is still cold, but the volume of air is reduced considerably. Is this normal? My question is, does my boat have a thermostat that regulates the airflow to control the temperature? I was under the assumption that the temperature knob was to control the temperature of the air coming out of the vent, not used like a thermostat. Does that make sense? Is there a problem with my fan/blower? Or is it normal for it to cut back on air flow as the cabin cools down?

I agree 100% will all the posts so far in this thread. There only a few things that would cause icing. Too low of a base temp setting, restricted air flow or low coolant in AC unit. Make sure no vents are closed and that they are in full open position. Check all vent hoses to make sure they are not crimped thus reducing airflow. Make sure your cold air return vent (big square one) is free from any obstructions and filter is clean. Bring down cabin temp in increments on hot days.

Where is you AC unit mounted?

[Guest]

Brad 3055 wrote:
You are freezing the unit up Cool it down in smaller increments. Check ur air filter, maybe you need more air.

+1

[Guest]

The a/c unit is under the V berth. The filter isnt clogged or blocked at all. You will have to excuse my ignorance but where is the coil? Is it viewable without taking things apart? And the water temperature of the lake is still in the upper 50's right now. Could the colder water be causing it to ice up pre-maturely?

[richardson]

You have hit part of your problem with the water temperature. Plus the fact you are trying to keep the boat too cold. Under your current conditions you are not presenting enough load on the A/C. The evaperator coil should be visible when you look in the compartment where the A/C is located. It will have fins like an auto radiator. Many times it is immediately behind the filter. If it is dirty it will also cause a problem.

[Guest]

As all above posts, the filter is probably right against the evaporator and will probably be covered with ice.

Often the duct work on these units will not accomodate enough air flow. If you notice it early enough just run fan only for awhile. That should defrost it.

You really need to manage the cooling by bringing the temperature down in steps.

[simo]

Have you determined if adjusting the temperature knob is cycling the compressor on and off? You may yet have a problem with your thermostat or improper placement of the thermostatic copper bulb.

[Guest]

not to hijack...but where is the valve people say to tap when the unit wont switch over to heat....

[Eyeman]

richardson wrote:
You have hit part of your problem with the water temperature. Plus the fact you are trying to keep the boat too cold. Under your current conditions you are not presenting enough load on the A/C. The evaperator coil should be visible when you look in the compartment where the A/C is located. It will have fins like an auto radiator. Many times it is immediately behind the filter. If it is dirty it will also cause a problem.

Bingo. A dirty evaporator coil or low refrigerant is usually the culprit. An icing coil might be caused by the cold condenser water or a mismatched load, but if that is the case someone didn't do their design homework when sizing the equipment (which could be because 65 degree in 20 minutes is usually way too fast). Good design would suggest under sizing the btu output and over sizing the evaporator coil. The match does a great job of de-humidification and handles maximum design conditions in almost all situations.

A few basics. When running an A/C unit, we first ring out the moisture from the air (latent cooling), then the temperature starts to drop (sensible cooling). If the unit is oversized we skip the first part and drop the temperature to quickly leaving us with a cold, high humidity environment that is not very comfortable or good for cabin equipment. I always error on the side of under sizing my A/C units. My 3000 square foot house is cooled by a 2 ton condensing unit coupled to a 3 ton evaporator coil. Sometimes the unit will run for hours before the temperature moves a degree. But the condensation runs like a faucet during that time. Dry and comfortable is the result.

[Guest]

Shouldn't we wait until the original poster verifies that the unit is indeed icing up reducing air flow? While everything posted related to an icing problem is dead on, and icing can well be the problem, if I'm not mistaken, at least on some units the fan speed is automatically slowed when set temp is reached. Might that not be the case?

[Eyeman]

captjmh is spot on. I have not heard of a fan slowing during a satisfied cooling cycle, but it's sure possible.

[Guest]

I am not at the boat but i will go back in the next few days to have another look at it. I will report back with results of my inspection and testing.