new air conditioner tripping gfi

Bad install,

With the new A/C they have either hooked the Neutral to the rest of the system's neutral or they chassis grounded it.. I do not know if a chassis ground will trip the GFCI, but I do know a common neutral will.

Is the GFCI worn out? More often then not in our area they are worn to the point they can hardly stay on. It takes repeated flipping of the breaker to get them to set. Also the earliest GFCI's had a hard time with big motors. They appear as a fault to the gfci (because of the rule of ELI if you care to look it up)
If that's not it then try it with the AC off. Also recheck the wiring to the AC, you may have wires reversed.

is this circuit for the a/c totally isolated from the MAins power,

this is the same symptom people get when when trying to use a 30amp and 20 amp parallel to get more power

the 20amp GFI is connected to the 30amp circuit
there is an imbalanced current flow detected and the gfi trips

Does it trip the GFI with the air conditioner circuit breaker turned off? If no, there's leakage between the hot (black wire) and chassis ground in either the wiring or the air conditioner itself. If yes, there's leakage between the neutral (white wire) and chassis ground in either the wiring or the air conditioner itself. Disconnecting both power wires at the air conditioner should tell if the problem is in the air conditioner or the wiring to the air conditioner. To be safe, just pull the shore power plug before working on the connections. If you're not experienced with 120 volt wiring, leave it to somebody who is.

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