hello, I have a 7 year old 2 ton ducane unit. 3 days ago I noticed my defrost wasnt working. tech came out and put a new defrost board on. he also put refrigerant in it (it was a little low but not bad). that night when the unit came on seemed to be working fine but when I got up during the night i noticed cool air coming out of my vents. I cut the unit of and cut it back on and the unit kicked on and then I heard a very loud grinding like noise wich it did 2 more times and finally the heat kicked on. after i called the tech out the next day he said he may have added to much refrigerant so he drained some and took the pressure. I go to bed and wake up to the same noise the next a.m. he comes back out and this time im bonedry on refrigerant. ive now got to change a reverser valve cause it has a leak. what im wandering is,is the grinding noise im hearing the compressor and is it going bad to.