why circuit breaker and fuses in same AC circuit? never seen in other systems I've owned, the breaker keeps tripping in todays 112 heat?

Actually a heat pump system... the breaker happens to be outside and is overheating or at least very hot to the touch and keeps tripping. there's a 60A in the main box in the house (chatters momentarily when AC compressor first comes on) , then a 50A outside (has no issues when compressor comes on, but is tripping in the heat and sometimes in winter when first switched to heat) a set of fuses at the outside exchanger/compressor that also a Supco SPP8e or 9E hard start cap installed

Just for kicks I checked the temp on the breakers with my Fluke IR thermometer... the 60A inside is just a few degrees above ambient, while the 50A outside is 65 degrees above ambient (162f) on one leg and only 30 above on the other. I guess I'll start by making sure all the wire lugs are tight, but otherwise I'm lost, a few weeks ago it ran problem free when daytime temps were peaking at 109 for a few days straight.