Condensor went, HVAC guy is blaming electrician, is this possible?
Per the National Electric Code (assuming you are in the US), #8 is for up to 40A, the Minimum Circuit Ampacity (MCA) was 32A, so there was no issue with the wire size he initially selected. The MCA rating is based on the 125% factors already, so you do NOT need to do them again if you already have that number available to you on the nameplate.

Bottom line, the HVAC guy is just trying to dodge responsibility for a defective product.

Also, a "buzzing" sound would not be coming from the breaker unless it was loose. That sound was likely the result of a failed starting capacitor.