Trane Xl1200

then the main fuse trips home. suggestions? device is at least 20yrs old

The circuit breaker 35 amp motor must be 125% to be 45 amps 40 amps, but it works until it gets old and it all starts to slip. You should not play with faulty breaker, call an HVAC company and get an offer on a new Trane high efficiency. There are rebates and tax credits offered in some cases at present and new units to save $ $ $ on energy costs. If not, call an electrician and get the problem fixed properly.

You have a kind of short circuit in the air conditioning unit. It does not bind or better. You need to have a qualified technician to come and find the component in short circuit and replace it. There are several electrical could be including the compressor, outdoor fan motor, capacitor, or a faulty electrical connection. Do not hold the breaker closed. You will only create more problems.