Heat Pumps and Electric Heating - frozen heat pump need help

Ok first i have a heil heat pump.My heat pump did not start getting frost or ice on it till this winter or when it started getting cold.Now i did have have a friend who had this happen and it was his defrost board so i called a tech and had them put a new one in since mine is still under warranty. This did not solve the problem so i called them back they checked the freon it was real low so the checked to see if i had a leak and i did.I was in on the coil in the heat exchanger or the air handler unit what ever it is called it was also under warranty so they got a new one i a week and came out and put it in and filled it with freon so i was happy the next morning i went outside to look at it and it is still doing the same thing.I don't know what else to do the labor is starting to add up alot.

does anybody know anything that will help me out.

when the tech replaced the defrost board did he also check/replace defrost t-stat? some come as a kit with both parts included , some come seperate. also is unit ( coil ) icing solid or is it in bands

I don't know about the t-stat but it is everything icing solid inside and out.I will have to ask him about the t-stat when he comes back out.

Basically what the thermostat and defrost cycle involve is for a specified time, your heat pump becomes an air conditioner, taking warm air from your house and running the warmed freon backwards through the tubing, defrosting the outside coils. This lasts for a minute or so. You will note the outside fan will stop and it sounds as if the unit will explode, but it is normal. Once the defrost cycle is complete it will restart, giving you heat.

Ok when the house get's to the right temp the fan on the outside unit does stop.Now with the defrost cycle does it sound like a vacuum sort of like air going through the lines.Is that the defrost?

Yep, it is actually reversing the direction of the freon, bringing the warmer freon outside to defrost the coils on the condenser. But, generally, the fan on the condenser will stop during this process, and start again as it reverses it self back into heating mode.

heat pump is fixed it was the sensor on one of the lines that tells the defrost board that it needs to defrost. Even if it just got done with a defrost cycle. Thanks for all your guy's help