Quote:
Originally Posted by jeff5may
CXR is short for chest xray seriously, cxr is short for compressor.
To help others reading this thread, I will share my learnings about defrost control boards. There are only a few OEM suppliers of these boards, ICM, ICP, and Ranco being the three largest. From these few manufacturers come hundreds if not thousands of rebranded control boards.
The simplest type of board is the ICM 300 type, aka 621 dash whatever, aka Ranco DT-1. They use a separate defrost relay. They get power from a defrost klixon thermostat, which clicks on at a set temperature corresponding to a frozen evaporator. The board delays defrost a set amount of time before initiating defrost via the relay. When the evap coil warms up enough to click off the defrost thermostat, the control board loses power, the relay is deenergized and the unit goes back to normal operation. If the defrost klixon isn't satisfied, the control board ends defrost after ten minutes. It starts timing again, and defrosts after time runs out again.
The type I bought has its defrost relay on the board. It also can be wired to run off a klixon thermostat, but it doesn't have to. It has a thermistor which does the same job without any moving parts. This one, an ICM 315, is the same as a Ranco E-15 or an Avion DFT-100. It isn't quite as universal as the above board, since it has only one set of relay contacts and a standard defrost relay has three. Otherwise, it works basically the same: preset delay time, check thermistor sensor, defrost if too cold. When thermistor senses warmth, end defrost and start timing again.
There are maybe a dozen basic variations on these two designs, tailored to fit more elaborate units. HVAC techs stock a few each of their preferred brand of boards in their truck and are covered for 99.9 percent of every unit they will encounter in the field. For the other 0.1 percent, one of the stock boards will drop in with a little sorcery or the customer can pay 500 dollars for the (rebranded) 15 digit number (same) board.
My opinion is this: if you want to make your own temperature controller defrost microcomputer, go right ahead. It can be expanded later to stream real-time chest x-rays of your unit to your iphone if you want it to. But the pros go with what works and what is common. When mother nature wreaks havoc on the world, that 5 dollar timer will probably survive. If not, tech comes and swaps board in 10 minutes for 250 dollars to get you going today. Or you can do it yourself for 5 dollars. Or you can spend countless hours trying to figure out why your microcontroller went insane.
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I've used the Ranco before and done many things to adapt defrost mechanisms to different machines and it is still a pain IF the goal is the lowest cost overall heating (best COP). One problem with trying to adapt an existing defrost control is that they are usually have some embedded safeties, for example, I tried to adapt an 18 seer York heat pump to have a liquid condenser but it was a 2 stage cxr (I should have been more awake when i asked that question
) but got no joy because the control would only recognize signals from defrost or indoor that it expected. Anything else and it would lock out.
This is why we are designing our own controller where we can change the PID to suit the situation and control pumps etc.
Back to the point......I like the idea of small pump as you have suggested. It really depends on how that water can be dumped on the coil in a logical manner.