I had my unit (air conditioner/heating)re-wired going thru the outside unit to the attic.My freon since has been leaked and the company wants to charge me $500 to replace the valve and re-charge they put new lines.Is it easy to replace the valve and then just have someone that has freon put it in. Or what can I do to fix it myself? I have already paid them over $1500. and don't trust them anymore? I hope you can help me? Any advice will be appreciated.