35000 BTU A/C freezing up

My mistake; it is a 13500 BTU AC, not 35000!

Here's what I've found that remedied the situation:

1. The insulation between the return air and cold air behind the filter in the ceiling had several voids in it. I repaired/recaulked/retaped these. This was probably causing most of my freeze up problem due to cold air returning to hit the evaporator.

The switch that is attached to the evaporator coil that shuts off the compressor when the coils start to freeze up WAS securely attached to the coil.

2. In 12 years, sorry to say, I'd never cleaned the coils up on the roof. I removed the evaporator protector cover and used a hose (carefully, so water didn't go down into the RV) and used somewhat low pressure to clean the evaporator fins which were dusty, but not caked with lint, etc.

3. I also used higher pressure (hose pressure @ 50psi) to squirt out the condensor coils, radiator fins(both sides), and water drain to the roof.

4. I carefully unbent several areas of condensor(radiator?) fins using a plastic spoon.

5. After this, I ran just the fan, on high, for about 30 minutes to dry everything out.

6. Before putting on the roof cover, I ran the AC for 15 minutes so I could determine if the suction line was cold (frosting), which it was. According to what I've read (including the manual someone posted a link to; thank you!) this indicates that you are probably NOT low on coolant. The manual says it is RARE for an RV AC to be low on coolant, unless it's been physically damaged It is a closed system from the factory, with no place to recharge it. If the AC has worked properly for quite a while, then the chances there's a leak or that it was a defective unit from the factory are slim. Look elsewhere.

Most research I've done says to keep your filter clean and NEVER run the unit without it. Set your thermostat

It is cool here today, so I can't really check everything out for cooling ability, but there is considerably more air moving through the vents now and I'm confident that the problem has been solved. If not, I'll repost. Thanks for the suggestions and help.

Try Chris Bryant's A/C Cleanup. If you have a wall thermostat your roof section should have a Defrost Sensor. If that Sensor is misplaced, the unit can also freeze up.

clean the coil on the roof.

run your blower fan constantly. this is what i do.

Do you have a WALL tstat?
No, there is no way to connect regular gauges
IF it was low on Freon, then you have a leak and ALL the Freon would leak out, so you will NOT get freeze ups due to low Freon. They only hold 16oz of Freon
As others mentioned, make sure the Condensor and EVAP coils are clean and free of debris.
The ONLY way to check state of the Freon charge is to use a clamp/on AMP meter to see what the amps the compressor is pulling corrected for the ambient temp. Doug

mmorris wrote:
Our 2002 Keystone Sprinter 28'fifth wheel with a single AC has been freezing up. It has happened before when we were in high humidity areas but we are in UT where the humidity rarely gets to 20%. Even before it freezes up, it doesn't seem to cool like it used to. It has been getting to the low 90's here but the AC will only cool to about 83-85. It seems to put out cool enough air in the first few hours and then the fan output lowers as well as the coolness; I suppose as it starts frosting up.

Does this mean it's low on coolant? If so, can I test this with the coolant refill gauge/attachment I use on our vehicles? Can coolant be recharged in these units?

Any other suggestions will be appreciated. We are in UT for another 2 months of hot weather:)

35,000 BTU is a bit of overkill to say the least. So my guess would be that you're attempting to throttle the A/C by keeping the blower on low speed.

Turn the blower speed to MAX!

I had the same problem on a 13,500 unit. Honestly a 13.5k is what he is referring to. the coil was full of******from pollen and mud dobbers and wasp nests, a simple cleaning and back in business.

I had a similar problem. My buddy is a heating/cooling guy. He told me freeze up is most likely caused by poor air flow over the evaporator coils. Lack of airflow doesn't allow the freon to boil off properly and absorb heat.

Check for air leaks around the coils, and blockages in between the coils. Replace your filter if you have one. Anything that will improve airflow will help.

Check the freeze sensor is inserted into the iced up evaporator.
Otherwise at 12+ years old in UT I would be looking for a new 15k unit.

Common issues causing evap coil to freeze:
Dirty filter
Dirty evap coil
Freeze sensor dislodged from evap coil

Common issues causing evap coil to freeze:
Dirty filter
Dirty evap coil
Evap coil freeze sensor dislodged