Originally Posted by Mr_D
Umm... I can run both 13.5 heat pumps off a 30 amp shore line. Have done it many, many times
You are comparing a single standard air conditioner that draws around 15 amps (thats nearly 30 amps for 2 of them) to a Dual heat pump system that may only run approximattely 15 amps total. If the dual normal AC did not overload the 30 amp supply breaker when one of the unts cycles on, add in the additional loads like a converter and just a TV and your way over the limit. The mfg designed the OP's system for the technology and price point that was available at the time it was built (1989).
In the OP's case, if the vacuum cleaner was running along with the converter then when the AC cycled ON, the high compressor start up current simply overloaded his system.
Just a simple case of limitations one must learn to balance for the system he currently has at his disposal.