Check that the air bag has & can still hold air, by putting some in via the Schraeder Valve under the seat - only put 20-30 psi in there & only use a quick shot of shop air, cos it's a tiny bag & the air will go in pdq! The max pressure for the bag is 90 psi, but if it develops a leak & empties then the compressor can overheat & die thru running all the time while trying to keep the bag topped up once the pressure gets low; or sometimes the valving will jag in & dump all the airtr then pull that 'manual' trick just cos the pressure IS low, in which case a little air pressure in there might let it all work properly once more! Mine's done that a couple of times, only to work properly again once there was starting pressure in the empty air bag! But it's also scored a leak fm a small tone stuck under the very bottom of the bag which killed the compressor, requiring its replacement, fixed the air bag by adding about 5mls of Slime to the bag, & it's worked fine ever since. Nb, if you need to replace the compressor, DO NOT get a BRP replacement or you'll end up needing to replace it again; instead, fit an a/mkt replacement, much more robust, cheaper, and continuous rated, so you'll never over-heat it AND you can use it to inflate your tyres too, all it takes is a T & a valve/outlet.... The VIAIR unit is one of the better replacement compressors. :thumbup:
Good Luck!