Hi everyone... this is my first post and hoping someone can help me out.
I live in a condo, built in the 80's. It has a heat pump system, Magic Chef brand which was probably original to when the condos were built.
The problem I have encountered is in the winter, in outdoor temps below freezing, when there is snow... the part of the hvac unit on the exterior of my condo forms ice on the condenser/coil. I can get it to defrost only if I switch it into A/C mode. So, that means that my reversing valve is working. When I bought the condo, I replaced the thermostat with a programmable thermostst (White Rodgers). I did notice it has an internal O/B switch on the thermostat. It is on the 'O' position. Would it make any difference or energize the reversing valve in heat if I switch it over to 'B'? The wire color looks dark orange, but not black.
I have also been told to check the defrost relay and/or defrost control/timer because it may be a part causing it not to operate.
Any help would be greatly appreciated. If you need any further info to help me out, feel free to ask.
Thanks

If your unit is heating fine than it is probably not your thermastats blue or orange wiring the blue is typically used toenergize the valve in heat and the orange to energize during cool mode you are probably looking at defrost thermastat or defrost relay or your timer. If you have a thermastat and it is faulty it will not close the relay to call for a defrost mode. Your relay is what deenergizes your reversing valve to allow for defrost.

I'll look into testing the defrost relay and defrost control/timer. Any info as to how I can go about testing those parts?
Also, the make model of my unit is:
Magic Chef
Model - PWC24E9.2-1

Does anybody know of any websites/companies which I could possibly find parts for this unit?

Thanks again

J Acosta is correct with his information, the parts needed are probably generic parts that could be purchased at your local heating and air conditioning supply house. The timer is a likely suspect, they will have a name and model number on it , the same with the relay. Good luck, Mike

Thanks... I appreciate the advice.