A/C Operation

Dave H M wrote:
mine has never froze up on low cool. 10 years now.

I did not say it was MY theory. only that I get slammed all the time for saying what you just said...

Dave H M wrote:
mine has never froze up on low cool. 10 years now.

Good for you. YOU don't work on them, I do. And have for 41 years. From RVP (Coleman). READ the last item. This is for mechanical Tstat systems, not wall tstat systems. Doug


What would cause my AC to freeze up?

To answer this question, you must understand; air conditioner capacities are rated primarily by their ability to transfer heat from the inside of your vehicle to the outside air. Your air conditioner may freeze up if it fails to pick up or transfer heat for any of the following reasons:

Indoor and outdoor temperatures may be too cold (lack of heat).
Evaporator air recirculation is possible due to poor or improper installation.
Airflow obstructions:
Dirty filters. Filters should be cleaned regularly.
Supply air louvers may be shut off.
Inadequate or damaged ducting (if so equipped).
Dirty or plugged cooling (evaporator) coils.
Low Fan Speeds (motor that is not pulling enough amps or airflow).
Improper Operation: Setting the temperature on the thermostat so low the compressor does not cycle off and on. Running the compressor and low speed fan together may cause “freeze-up” conditions to accelerate.

mine has never froze up on low cool. 10 years now.

It depends on your AC type and controls. Do you still have the 1999 KSDP? If so, do you have the 4 button or 5 button Dometic AC tstat control? Do you have an HP or AC only. If you have the 4 button and a HP and you run on LO cool, the AC will probably freeze up as the 4 button did not have a freeze sensor. The 4 buttons could not accept a freeze control. That is one reason Dometic went to the 5 button wall tstat in 2001 and dropped the 4 button. Also, how many units do you have on the roof? Most KSDP had 2 roof units. BUT 1999, Newmar failed to install enough return and exhaust round ceiling vents. Your unit requires 18 round ceiling vents. 9 intake and 9 exhaust. If you do not have this many your unit cannot adequately cool correctly and WILL freeze up.
Now, to the original question. IF you have a WALL TSTAT, then your roof AC has a freeze Thermister. So, operation is up to your preference. Auto means it will run on HI COOL and as it gets closer to set temp it will go to lo COOL and then shut off the fan and compressor when it reaches the set temp. Now, if you would rather have the FAN run continously either on HI or LO to circulate air all the time then set to HI cool or Lo COOL, and the compressor will cycle on and off, but the fan will always run at the set speed.
If you have mechanical roof mount AC controls, then on LO cool the AC WILL freeze up in hi humidity or higher ambient temps as Mechanical controls have no freeze control. HI COOL keeps the freezing from happening. Doug

I have heard a lot of yammer.. HIGH COOL is my choice.. And here is why.
The fan on auto will cycle between low high and off. this is very annoying sound wise as you hear every change and never "Filter" the sound out.

Fan on constant HIGH your brain quickly filters out the sound and it gets to the point where you do not even notice it (or at least MY brain does that. NOTE I have Ducted A/C's)

Next is an argument I often get in.. What causes the A/C Evaporator to ice up?
One theory is low air flow caused by either one or both of the following:
Fan on LOW and dirty intake filters.

That is not MY theory but it does appear to have some truth.

So HIGH COOL is my choice.

A/C on. Fan on AUTO. That will cycle the whole unit and keep the humidity down. I run the fan on low fan to keep noise down. That's how the A/C in my house in Florida works also. Most people don't know that fan on auto will keep the humidity down.