Heat Pump

just had a similar problem, the smell was the compressor capacitors not storing voltage properly to assist in the starting of the compressors. then one blew apart, the oil from the capacitor was all over. stinking, it melted 3 wires together causing more damage to printed circuit , fan capacitors and wiring harness all had to be replaced with the unit pulled out by shop here in NC 1200.00 bucks. reason either low voltage or a bad capacitor , who knows?
Good luck and turn both breakers off comp 1 and comp 2 if its a coleman-Mach.
website for them is RVP products, or Airxcel.