OT: room air conditioner

You have a real problem here. Typical air conditioners are designed to drop the temperature of the air flowing across the evaporator coil by a certain number of degrees. If the incoming air is warm enough then the hear transfer will keep the evaporator coil above freezing. Once it stars to freeze then it enters a death cycle. The first bit of frost restricts the air flow. The reduced air flow reduces the heat transfer. The coil gets colder. More ice forms.

You have a few (bad) choices here;

• Increase the air flow across the evaporator coil. This will get noisy.

• Decrease the thermal flow in the freon system. Possibly by slowing the compressor. Don't know a good way of doing that. Decrease the efficiency of the condenser coil by restricting the airflow. This won't help your electric bill.

Pete.

The evaporator should not freeze up .I think they did not put enough freon in the system to keep the evaporator above freezing or you have a small leak.The less freon you have in a ac system the colder it gets (to a point) When it gets to cold the water around the evaporator freezes and blocks all air flow . . Turn the fan on high the more air moving across the evaporator won't let it get as cold and the the less likely it will freeze up.If it stll freezes up you will have to add a little more freon to it .This will raise the pressure inside the evaporator and it won't get as cold.You don't want the evaporator to get below 32 deg. because you get freeze up. The temp sensor in frount of the coil is for the room temp.Not the coil temp. it just cuts the compressor off when your room gets to your set point and on agian when it gets a few deg above it.

Most of these are capillary tube/bulb expansion principle, not a thermocouple.

Sometimes they have coarse range adjustment cut-in/cut-out screws inside, the user knob being essentially a relative fine-tuning adjustment.

A freezing evaporator is a paradoxical sign of a low refrigerant charge, which is common, especially in older units. I know they're supposed to be sealed, but somehow it happens. Paradoxical, because you might expect a low charge to result in a warmer evaporator, not a freezing one. But what happens with a low charge is that the very first portion of the evaporator (only part that gets liquid refrig) is too cold (low charge lowers suction pressure) and freezes, and the rest (most) of the evap is warm; the freezing creeps further and further across it as the ice builds up and insulates the first portion, until the whole thing is progressively frozen.

It may also be that the unit by design cannot cool down to 55 deg F without freezing up. Obviously there is some limit well above freezing to what it can deliver, because it isn't designed to defrost itself like a freezer. Since you typically have a 20 deg difference in input vs output air, and 32 + 20 = 52 deg F, plus some safety margin, means 55 or

60 is doubtful.

If you want 55 deg F setpoint, but the thermostat doesn't control that low, you can get a plug-in control for that temp that switches the whole AC outlet, and hot-wire the unit thermostat. But you need to fix the freeze-up first or nothing will work.

Oh one more thing to add .Runnig the ac when its cool out side will also lower the evaporator temp. and could cause freeze ups.

Understand this is a new unit. The reason it freezes-up is I have routed the temp sensor away from the coil and into a tin can heated by a light bulb in order to "fool" the sensor and keep the compressor running. If I put the sensor in it's holder on the coil, the unit works fine...I just want it colder.

I follow you, but the possible reasons are as I stated. In short, an air conditioner won't perform as a refrigerator. The delta T runs into freezing at about 55 deg F ambient and the evaporator ices. Assuming it working right, with a low charge it is even worse.

You could trick it up with defrost controls, but that will turn it into a real science fair project.

Fit a more powerful fan.

Mark Rand RTFM

I have serious doubts this is going to work. If you really wanted to do this, you should have selected an industrial refrigeration contractor and paid him to design a custom system for this purpose. Home A/C gear is just not designed to chill a house to 55 F. A specially designed system with an accumulator and thermostatic expansion valve, and the evaporator unit properly sized for this temp range should handle it without a freeze-up.

Many window units of old would do this well, but the newer energy-efficient units probably are not as flexible. One possibility is to get a truly massive window AC (I think this is what we're talking about here with the

12K BTU unit) that will run very short cycles, and the coil will have time to defrost between cooling cycles. Keep the fan running all the time to do that defrosting between cycles.

There is no evaporator "sensor" on window AC units, or even on most central AC. They use what is called capillary tube metering of the refrigerant to the evaporator. This is essentially a constant flow, no matter what the temperature or load on the system. Higher-end equpment uses thermostatic expansion valves to regulate refrigerant flow to keep the evaporator nearly full of liquid, but not permit the compressor to be assaulted with liquid.

Some newer AC may use thermistors for temperature sensing, most older ones used a bulb filled with some refrigerant gas and a bellows. The evaporator is very unlikely to have any active regulation of refrigerant flow, just the cap tube. A thermostatic expansion valve (TXV in the trade) would help get optimum cooling from the system, but really won't help a great deal with the freeze-up problem. Keeping the evaporator nearly full of liquid may even out the cooling over the entire evaporator, though. If the freeze-up starts at the bottom of the evaporator and slowly works its way up, then the evaporator may be running dry under the cold conditions you force it to run under, and a TXV and liquid accumulator might help it not freeze. But, that's a big maybe.

Jon