The cooling test sequence for this board, says to jumper Y & G to R. Make sure the fan comes on, and spins up to the proper speed. Then remove the jumpers, and check the fan off delay.
If the blower does not come on, verify that the COOL terminal is energized. Use a voltmeter between COOL and neutral, and verify 120 volts (with jumpers in place).
If the COOL terminal is energized, check the motor and verify all speeds are working properly.
If the COOL terminal is not energized, the board my be bad.
According to the schematic you've provided, you have a multispeed blower (which is quite common). The speed at which the motor runs, is determined by which wire is energized. Energizing the red wire; for example, will run the motor at low speed. Energizing the black wire, runs the motor at high speed.
Before you disconnected the board, one of the motor wires was connected to the HEAT terminal on the board, and one was connected to the COOL terminal. Looking at the ladder diagram, it looks like the blue (MED) wire was connected to the HEAT terminal, and the black (HI) wire is connected to the COOL terminal.
If you've run the tests described above, and found that the COOL terminal is energized when the jumpers are in place. You can try connecting a different speed wire to the COOL terminal. If the motor spins up with the other wire connected, it means that the original speed is dead or something's wrong between the board and the motor.
It looks like the LO speed red wire is attached to the M1 terminal on the board. I'd swap that to the COOL terminal (just temporarily for the test), and see if the motor spins up when the jumpers are in place.
WARNING: DO NOT run the A/C for long with the motor at a lower speed..
There are a multitude of blowers out there. The outside breaker you mention likely has no relation to this problem. The pipes are indeed freezing due to too little airflow. Here are the most likely causes and solutions for this:
Assuming you have one of the most common PSC types (and not some other type like an ECM, slip induction, etc), then a weak run capacitor for the blower motor can cause this problem. The run capacitor for the blower should be checked with a capacitance meter and replaced if it is below 90% of the rated value. Or, if you happen to know how to use an ESR meter, then check the capacitor that way.
It is possible that it is a multi-speed motor with the wrong lead energized in the "cool" mode. Typically Red=Low, Blu=Med, Blk=High. The black lead is usually the one needed for a/c operation.
Sometimes the motors wear out by having the lubricant in the bearings go dry. In this case the blower wheel will not turn effortlessly and smoothly by hand when the unit is off. If the bearings are dry, then you need a new blower motor.
(unusual) Since you have a heat pump, if it is a higher performance model it may have an electronic blower speed control that is supposed to automatically slow the blower when it is very cold outside to ensure an adequate warm air temp inside. Typically, this would be shunted to high speed blower mode for a/c operation, but if a control relay has failed or appropriate wire become lose, or other fan speed control failure has occurred, then the speed control could be causing the blower to run very slowly (as it would in cold weather heating operation). If you have this then you will have to determine if it has failed by temporarily bypassing it to see if the fan runs on high speed without the speed control unit inline.
Verify main power for the unit is off before proceeding with any of this work. The main power for the air handler is usually separate and in addition to the main power for the outdoor unit.
**Edit: I see that Ducane air handlers offer options including both electronic blower speed controls as well as constant torque (ECM) motors. If your unit has either of these then the low speed problem may have other causes. For example, ECM motors have an electronic digital driver that is set using DIP switches or other means. An incorrect low torque setting yields low blower speed. I recommend you post the exact model number of your air handler as well as a photo of the interior showing the back end of the blower motor and the control board. A close up of any DIP switches as well as a legible photo of the schematic on the inside panel would be nice too if you want any additional comments.
Best Answer
Yeah, your control board is shot
I'd replace the control board if I was in your shoes; the behavior you are seeing is a sign that the relays on the board that control the blower motor are failing, or something is causing it to drive them uncommandedly for that matter.