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jeff5may · 12-25-14, 03:15 PM

If you want or need to actively control the defrost cycle in your machine, there are a number of premade boards available for cheap. The two main manufacturers of these boards are ICM and Ranco. The control boards of both manufacturers cross-reference directly to each other, and to a zillion rebranded proprietary part numbers.

My two favorite defrost boards are the ICM 300 and the ICM 315. They can both be found on ebay for around 20 dollars just about always. Depending on how you are going to assume control of your unit, one or the other will do a better job than the other. When installed correctly, they both serve as industry-standard devices as to reliability and performance.

The ICM 300 is a truck-stock item in service trucks, due to its popularity and flexibility. It has been integrated into millions of heat pump units over the years. It is made to be wired in series with a bimetal klixon thermostat, receiving power only when the thermostat is active. It wires to a separate "defrost relay" which in most cases looks like an ice cube.

The virtue of a separate defrost relay is that you may rig the relay contacts so they force whatever mode of operation you want to command during the defrost mode. This type of control can be recycled through several revisions or machines, and will operate like you wire it pretty much flawlessly forever.

The ICM 315 has its own, onboard power supply and control relay. It can be rigged to either a bimetal switch thermostat or a thermistor, depending on how you want to do your defrost. This one works well with the passive defrost units described previously. If you figure out some wiring details, this one can be rigged without any extra devices to enforce defrost control.

12-25-14, 03:15 PM	#14
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	If you want or need to actively control the defrost cycle in your machine, there are a number of premade boards available for cheap. The two main manufacturers of these boards are ICM and Ranco. The control boards of both manufacturers cross-reference directly to each other, and to a zillion rebranded proprietary part numbers. My two favorite defrost boards are the ICM 300 and the ICM 315. They can both be found on ebay for around 20 dollars just about always. Depending on how you are going to assume control of your unit, one or the other will do a better job than the other. When installed correctly, they both serve as industry-standard devices as to reliability and performance. The ICM 300 is a truck-stock item in service trucks, due to its popularity and flexibility. It has been integrated into millions of heat pump units over the years. It is made to be wired in series with a bimetal klixon thermostat, receiving power only when the thermostat is active. It wires to a separate "defrost relay" which in most cases looks like an ice cube. The virtue of a separate defrost relay is that you may rig the relay contacts so they force whatever mode of operation you want to command during the defrost mode. This type of control can be recycled through several revisions or machines, and will operate like you wire it pretty much flawlessly forever. The ICM 315 has its own, onboard power supply and control relay. It can be rigged to either a bimetal switch thermostat or a thermistor, depending on how you want to do your defrost. This one works well with the passive defrost units described previously. If you figure out some wiring details, this one can be rigged without any extra devices to enforce defrost control. Last edited by jeff5may; 11-16-15 at 06:21 PM..