Window AC Restarting Again and Again

Could it be that the heat load applied to the pair is only just over the capacity of one machine, i.e. the machines are operating "duty/assist"?

The problem is most likely that the AC system is oversized for the actual heat load in service. You have most likely sized it based on the maximum heat load it could see instead of what it is actually seeing. Try moving the thermostat from the air plenum and instead connect it to the heatsink of the power electronics instead. In that way it will be reading the temp of the electronics, not the air coming out of the plenum.

You may find you'll need to divert some of the air elsewhere through a solenoid operated damper so that you can close it with your PLC if you ever discover the unit needs full cooling capacity, perhaps to the operator's station to keep him cool, or to the cabinet of another machine nearby.

It sounds like you should have sufficient load for that capacity AC unit. Several factors can result in short cycling of the compressor.

First I would make sure that the supply air has free discharge into the area, and verify that it is not being reflected back at the return air and temperature sensor. It is unlikely that the unit could cool the area in the timeframe you specified.

You didn't say if you've been monitoring the actual temperature of the room, so the possibility also exist that there is a malfunction with the AC unit. Depending on the type of unit it may be possible to adjust the differential that is the cut and cut out temperature spread of the factory thermostat. If that is possible increase the differential.

Another possibility would be to install a remote thermostat with the temperature sensor located in another part of the room. Without more information my guess would be either restricted or reflected airflow.

Good point, I assumed that the unit had been installed with unrestricted airflow, that might not be a good assumption.

At this point I think we're all making a lot of assumptions, I'm assuming it's a cheap Home Depot type window banger. One thing I should have added to the post is to run the fan on high speed that solves two problems at once.

Generally the evaporator and condenser fans share the same motor, so you can increase the airflow in the room and lower the head pressure at the same time. Although I doubt a high head pressure could be his problem, a overheated compressor generally requires 15 minutes or longer to reset, of course you never know the increased use of electronic safeties make generalize statements a real assumption.

It's also possible that you have moisture in the system and it's freezing up after 30 seconds or so.

If the AC unit has leaked some refrigerant charge, it may be short-cycling on its suction prsessure cutout.

As a previous post notes, even a small amount of moisture in the system can freeze in the expansion valve. This blocks refrigerant flow, and then as before the suction pressure cutout turns the unit off. This allows the ice in the valve to melt, so you can get a repeated cycle like this.

Finally, the air flow may be "short-circuiting"; i.e., returning quickly to the air intake rather than blowing throughout the whole space. This will trip the thermostat, which is usually located in the air intake. Relocating the sensing element, or the whole 'stat, may help (as already mentioned.)

Dear Friend,

See if following is of any help:

1. Take 1 ton for area of 25 square meters at room temperature between 30 - 35 deg. C.

2. Calculate the total electrical energy consumed inside the room. Take 3.142 KW for 1 ton and 400 BTU per person. 1 ton = 12000 BTU.

Regards.

Dear Friends;

Thanks for suggestions. I installed a temperature controller with prob and set lower limit at 22C and upper limit at 33C and found the AC working well.

Maybe, but I am glad I am not working in that space.