Hello,I am a retired mechanical engineer with 56 years in this business. I will go in depth with you, and up to a 6 hour time limit.
All I ask is please select the ***RATING LINK*** at the top of your page before leaving, that is the only way I am credited through the site.
Rating does not affect your charges nor ability to refund if not satisfied. If you can agree to that, lets continue by all means.
DEF usually means 'defrost' and it applies to heat pump type AC systems, if you can give me the brand and model number of the unit that sits outside I can see what you have, we can go from there in 6 hours, I am off to bed its late here.
There are no other HVAC experts on line here tonight apparently. However if you want faster service there is a chance that someone else will log on and help you before I get up....in that case just opt me out so that your question goes back up on the board.
If you work with me you will need a multi meter and may need to send me a photo of the unit wiring diagram if the manual for your system is not on line.