Air Contitioner Freezing Up

[HawkeyeFlyer]

I have a Dometic Marine Air unit, model number - VCD16K/2-LH. It works fine but eventually, after a couple hours, the heat exchanger ( the thing that looks like a radiator) will freeze up. It becomes a solid block of ice. Can anyone tell me why this is happening? I’m thinking it may be low on Freon. I’m not sure how to test it or if it can be recharged.

 

[uncledom]

I'm pretty sure this is actually caused by airflow over the evaporator (the cold coil radiator thing) or rather the lack of it. Make sure someone hasn't closed off a few ducts because the cold air was blowing on them. Just a first place to start.

 

[Jim26m]

Poor airflow or low refrigerant charge. As post above indicates, check airflow first. Dirty coil, dirty filter, restricted ductwork, dampers closed (per post above), all good things to check.

If you can't find an airflow issue, it's probably undercharged.

Could only find a bad photo of that unit In a quick search, but appears that it may have ports for checking/charging.

If you aren't skilled in this area, I suggest you sub the charging out to a refrigeration mechanic.

 

[HawkeyeFlyer]

>Poor airflow or low refrigerant charge. As post above indicates, check airflow first.
>Dirty coil, dirty filter, restricted ductwork, dampers closed (per post above), all
> good things to check.

It’s not an airflow issue. I’ve cleaned it and even placed a fan to blow air through it. It still freezes up.

>If you can't find an airflow issue, it's probably undercharged.
>If you aren't skilled in this area, I suggest you sub the charging out to a refrigeration
>mechanic.

Unfortunately finding a “Refridgeration Mecanic” that will come out to Rathbun Lake is proving to be difficult.

 

[Jim26m]

Sorry you're having trouble finding support. Do you have a friend, or friend of a friend, that does residential AC service? They should be able to take care of it if they're willing.
Problem is, you have to buy refrigerant that is compatible with the unit. Then, you need to have gauges to verify the operating pressures, or at minimum, you need to weigh-in a new charge. If this system uses R-22, you need to find some (not produced, but some stock is still available) or one of the substitutes that is suitable for top up. In my state, you have to have certification to legally buy it.

If it was 134a, you could go get one of those charging cans almost anywhere, with the built-in gauge, and take a stab at it. This is unlikely.

Can you tell what refrigerant you have?

 

[SEMPERAVANTI41]

I solved this problem by turning off the automatic fan speed and keeping the fan speed setting at a medium speed. Also some controllers have a "defrost" cycle available, which turns off the cooling and operates the reverse cycle by a timed cycle.

 

[JamesG161]

It is very rare to loose refrigerant.

Raise your thermostat temperature to 80°F or a point that the Fan still blows, but compressor shuts off.

If you cant get the compressor to shut off, you may have a thermostat problem.
Jim...

 

[jamieFL]

If it is freezing up, it is low on freon. By adjusting the fan and cycling through a defrost, you are only buying time. Look for an ac company that services commercial ice makers. They will go anywhere and should be qualified to diagnose any ac problem.

 

[gettinthere]

It's R-22. Be cautious about just topping up. Some refrigerants (I THINK R-22 is included, but not sure) are '2 part'. If you just top up you will likely only get one part and thus change the balance between the two parts. Do some research before just topping up.

 

[JRacer]

Mine will generally freeze up when I, inadvertently, or someone else who does not know the drill, set the T-Stat way too low. When I do that, the AC unit never cycles - it's just running continuously. Because it never cycles, the coils never have an opportunity to warm up. My solution is to turn up the T-stat for 10 minutes or so to thaw things out and then turn it back down but not so far. From there, I can keep cranking it down a little at a time as the temp in the room keeps coming down. I have not had the opportunity to get a tech out there to check Freon levels (R-22) as I have run into the same obstacles that you experience in that regard. But, because it is a closed system, low Freon would mean there has to be a leak somewhere!

 

[Jim26m]

R22 is not a blend.
The unit is "packaged", and is less likely to leak, but is not perfectly sealed. Depending on the age of the unit, even a packaged unit may need topping off.
However, good points above. The unit may have leaked down over time, or may have developed a leak. Hopefully, it has just squeaked out over time, but until you get it topped off and running correctly, it will be hard to tell.

 

[Brian D]

I trust you when you say it is not air flow, but having installed multiple A/C units in 2.4m satellite dish radomes on cruise ships, we found that the hot air from the A/C was being sucked back into the cool air intake causing the same problem.

 

[Terry Cox]

Our reverse cycle heat pump will freeze up when I forget to open the sea water through hull valve.

 

[JamesG161]

The 16K Dometic unit, if in AUTO Fan, will run 24/7 with the Fan. They use a Rotary Compressor from Tecumseh®.
Mine uses R-22 and the only way for it too Cool is to have the compressor running.
The refrigerant is NOT leaking or no Cooling at all.

What happens is after 10 of Billions of cycles, the compressor oil basically decomposes and is filtered out, not much decomposition of R-22.
The make up Refrigerant is a mixture of oil and refrigerant.
____
There is a tag on your unit that tells you the ounces of charge, the refrigerant, and the Amp pulls. It is on the top of your unit or inside the lid of the power box.
Jim...

 

[Rich Stidger]

Freeze up of the evaporator coils is a very common occurrence. I believe this is even covered in my user manual.
My A/C unit is a Marine Air Systems, but the issue is the same. On days of high humidity, the condensation from the air on the coils slowly freezes and builds up to the point that air cannot get through the coils. I suppose this low air flow could be hastened by vents that are partly closed or a very dirty air filter, but even with a clean filter and wide-open vents this condition will occur.
If your unit is a reverse cycle model, simply put the unit into heat mode (turn up the thermostat) for a minute or so. This will pump hot gas into the evaporator and melt the ice very quickly. Then switch back to cooling mode. Repeat as required.
If your unit does not have reverse cycle capability, then you need to turn the unit off and wait for the ice to melt.
For me this only happens on very humid days.
IMHO this is not a symptom of low freon charge. And should you ever decide to add freon to your unit, be sure you are not overcharging. Richard Kollmann is an excellent source of information for refrigeration units, and he will answer your questions personally. See http://www.kollmann-marine.com/ He also has a book that has lots of info to help you.

 

[JamesG161]

IMHO this is not a symptom of low freon charge.

Mine never freezes up since my drain pain is free to flow out.
All Dometic/Marine Air units are reverse cycle units.
_____
One last suggestion is to add a 1" Chlorine tablet to seawater suction strainer to clean that heat exchanger.
Low heat removal by the sea water can cause the "radiator" part to freeze up.
Jim...

PS: The Dometic sea water exchanger is the same materials used in Swimming pool or spas that see Chlorine.

 

[SEMPERAVANTI41]

As far as low freon is concerned, I had the exact same condenser icing problem with the original Hunter factory installed unit and the replacement Dometic unit I installed last year.

 

[jamieFL]

The two most common causes of a freezing up a/c is inadequate airflow, and low freon charge. A common misconception is that a low charge will cause the a/c to automatically blow warm air. Low refrigerant levels make the coils too cold...to a point. Then the a/c will stop cooling as it leaks down further.

Also, you do not necessarily have to have a leak to cause a low charge? Why do you think that they recommend an annual tuneup for your home a/c? They clean the evaporator coils, scold you on not changing your air filters enough, and top off the refrigerant if needed.

If he has good airflow, the next likely cause is low Freon... And that goes to everyone else that has an older a/c unit that is fiddling with the thermostat to prevent freezups.

 

[JRacer]

Good to know! Now, if I can just get a tech out to the boat to check it/top it off it might solve my problem. Thx.

 

[JamesG161]

I had my 16K unit checked out by the most modern Tech gauge system I have ever seen!
No matter what you do to connect up a test gauge you lose refrigerant.

The AC tech finally had all his instruments connected up, but his temp connections were too close to the sea water exchanger inlet hot refrigerant. Bad readings.
Finally he put that temp connection at the right spot and read his "computer info".

Me: Do we need to add R-22?
Tech: No.
Me: Well you released some R-22?
Tech: Absolutely NO R-22 needed!
Me: How can you tell?
Tech: The compressor has the right amount of superheat.
Me: Amazing technology.
Me: So when you do Landlubber units, you know when to add refrigerant?
Tech: True and we rarely have to add any. Adding can hurt your unit performance!

_____
On any unit there is a "Receiver" or a small tank that has reserve refrigerant. You would have to have significant leak to loose it. Low refrigerant would be the last thing to check.
____
Jim...

PS: Today if a Tech said he added Refrigerant I want to know where is the leak.