AH Heaters

[al perna]

The AH controls the fans at the registers and turns them on when it gets a signal from the thermostat for a particular zone. If all else fails take the cover off the AH and make sure the ice-cube relays are well seated, sometimes they work themselves loose. The ice-cube relays receive a signal from the tstat and enable the zone circulating pump and fans accordingly.

Would the above quote mean, that if your heater only runs on low speed that the Ice cube relay is bad ? In preparing for winter I ran the AH this morning for a test and to take out the chill . I was reminded of a issue last winter where I could not get the fan to run at high speed at all .
I tried changing the thermostat
Raising the temp

any thoughts ?