Most 240V appliances work fine down to around 200V since they’ll often be used with nominal 208Y120 power after voltage drop.
Are you sure you have 240/120V split phase service and not 2 legs of 208Y120?
If so, I’d contact an electrician or the utility company - sounds like the problem is upstream










Standard is for US buildings to be supplied with 240v center-tapped (single-family), 208Y120 3-phase (light commercial/multifamily), or 480Y277 3-phase (large commercial, light industrial).
120V is never supplied on its own.