Oh man good thing it wasn’t a 120VAC tstat!
I’ve come across some good design issues, best was a new house with the thermostat directly in a registers airstream. Heat would come on for a minute and shut off even though set at 80, thermostat was happy but the rest of the house was freezing.
My first install on a new job was a conventional 25 Ton Roof Top Unit that was being used to supply single pass air to a laboratory.
The lab needed the cooling, but could only take about half of the airflow from the unit, because it was balanced with the fume hoods. So the designer simply ducted half of the airflow directly back into the outside air supply plenum.
You can guess what happened next.
When the outside air reached 75 degrees, the unit called for cooling, and supplied 60 degree air. As soon as the unit turned on, half of the cool air was ducted into the fresh air supply plenum, and the controller detected a mixed air temperature of 68 degrees. The unit then went into economizer mode and shut off the compressor. As soon as the cooling was off, the mixed air temperature went back to 75 degrees, and the unit turned itself back on.
The cycle time for this disaster was about 55 seconds.
So our single-stage 25 ton DX system was turning itself on and off every 55 seconds, and slugging the compressor with each and every cycle. Equipment that was designed to last for ten years lasted about two hours. The mechanic bought a new compressor, rigged it to the roof and installed it, and the new compressor lasted about two hours.
I tell you, ya’ can’t make this stuff up!