My Goodman heat pump model CPLE48-1A will not go into defrost. I have replaced the defrost board and the defrost thermostat located on the outdoor coil. Any hints as to what to check next?

Test the coil (s) on the defrost valve. The defrost valve could be hung up.

Never heard of a defrost valve. Are you meaning the reversing valve coil? If so it does reverse to cooling when you set the t'stat to cool.

Thanks for your answer.

I've never seen one iced like this one was. The whole top grill was over 1" in ice. I wish I had taken a picture to show.

Check the part numbers you installed here

http://www.johnstonesupply.com/Portals/123/Member_CPLEHEATPUMPREPAIRPATS.pdf

It is always possible the thermostat was bad out of the box or not tight to the tubing which causes a bad reading.

Have you kicked it into defrost manually and made sure the coil is completely clean before putting the unit back in service?

Try these on for frost/ice up.

Well, it turned out to be multiple problems.
1st problem was a broken wire that prevented it from going into defrost. Broken off inside the wire nut and corroded so it wouldn't make contact.
2nd problem occurred when I went to the goodman parts house and bought a replacement fan blade for the condensing unit. It was cracked when the unit iced up. The replacement blade that they sold me was 3.5 inches smaller in diameter and let too much air bypass around it when the unit was running. I had to go to another parts house to get the correct diameter blade.
As of yesterday morning everything was hunky dory.

Thanks again for your help.

MERRY CHRISTMAS!