Hi all! Just got my first tub, it's a Leisure Bay 10000, built in 1995. It has a convertable ProShield control pack.

The previous owner had it on 110 and complained about lack of heat. I hooked it up to 220. Main 50A breaker to a disconnect box with a 50A GFCI, then to tub. All wire is 6/3+ground solid copper. There's a GFCI (20A only I think) and 20A fuse in the control box. See schematic below.

The problem is when I toggle the 110V/220V switch to 220V, the internal GFCI trips. All components run fine on 110, blower, pump, circulation pump, light; all work as expected. Not sure about the heat since I didn't let it run long enough to get to temp. It's drained now (first fill was for cleaning and finding leaks).

My question is: Is there anything else required to convert these babies to 220, other that flipping the switches.

I've spent some time troubleshooting already:

I've replaced the 30A/50A switch and the Auto/Timer (heat) switch, there was no continuity accross the terminals.

I've rung out the Voltage Conversion Relay, continuity switched from upper to lower terminals when 110V/220V switch switched and lower 6 terminals unhooked.

The inside of all contactors look brand new and have continuty accross when hand actuated.

20A fuse, Pressure Switch, High Limit good.

Heater has 11.5 Ohms accross terminals with wires removed, no continuity between case and terminals

Apparenty the schematic on back of panel (attached) is wrong or someone rewired it. L1 and L2 go to the Voltage conversion relay first, then the 30A double Contactor.

I've been at it for a week now and I'm running out of ideas, any help would be greatly appriciated. Thanks in advance!

Also, I was playing at lunch and rewired the Voltage Conversion Relay incorrectly, the grunda pump got hot and stopped running. Wired it correctly and it's still not working, I hope it has a reset and I didn't send 220 to it accidently. Would they seize if run with out water for 15 min?

Probably the T-92 relay

I've heard having two GFCI in series can cause one to trip. Would bypassing the internal GFCI by connecting common color wires be safe and a good step in troubleshooting?

no

The fact that it tuns fine while in one position, but trips while in the other strongly suggests the GFCI's are working properly.
Having 2 GFCI's does not cause random tripping.
The T-92 relay is likely your problem.