First post but Ive followed this site for a long time. One of my customers has a gravity fed 8x8x8 walk in cooler using MP-39 with remote condenser. The liquid line solenoid is controlled by an air sensing thermostat mounted on the wall about 6 feet up. The remote condenser is shut off by a low pressure control Im in Colorado so it gets pretty cold.
The problem has been, as long as they can remember, is that the evaporator coil would freeze up fairly often and keeping an even product temperature has been very difficult to obtain. I installed a defrost control and at present I think it defrosts 3 times a day for 45 minuets. After installing the timer the coil no longer freezes up but a constant temperature is still a problem. Apparently very slight changes in temperature result in too warm to freezing of the product.
Im looking for suggestions on how to correct this problem. Ive thought about using a constant cut or a Johnson Controls A419ABC thermostat with the sensor placed in the evaporator coil [best location for bulb placement] or using another low pressure control . When the 419 first came out if I placed the sensor in the evaporator coil it seemed to have a short life span and I quit placing them in the coil. Any suggestions would be appreciated.