The two relay LD 15 board is used with a HEET Recovery system which has a single speed motor that runs on 110 volts only. There is
no heater, just a heat jacket that surrounds the motor which captures the heat off the motor when it's running and transfers it via
the water running through the jacket. The board has two preset filter cycles, one at 8 AM and the other at 4 PM and run for 15 minuets
on each cycle. These times are not adjustable. The first version of the LD 15 boards only had one relay and a 4 pin transformer receptacle
which were upgraded to meet UL and CSA updated specifications. The old 4 pin transformer can still be used with the newer boards by
adding the 4 to 8 pin adapter . Typical examples of serial number that contain this style board would be PTDULD15...or PTAXDXLD15.
The very first HEET Recovery system was called an HR 10 which had an air button to operate the On / Off function. This system has
been discontinued some time back and would need to be upgraded to the LD 15.