Did they work before, aside from the hot/cold thing?
Could be several things, fortunately trailer drum brakes are one of the simplest mechanical assemblies on a "vehicle."
First, if it appears that none of the brakes are working at all, then greater chance it's the power supply, wire, trailer plug, even brake controller, somewhere upstream of the individual brakes.
Other things.
Could be all are mis adjusted very loose and not enough travel to even engage.
Could be bad magnets, shorted wire to a brake.
There are many published diagnostic procedures, if you're actually trying to diagnose yourself rather than just haul it back to a shop.
Hope ya get it figured out easily!