heater fan

[tommy mahaffey]

I got my modine ng heater working ,it has a 110 volt operating system on it.the gas and thermostat is working. problem now is the fan keeps cycling on and off about every 30 seconds. i changed the thermodisc out,same thing happens.
this thermodisc has 3 wires on it,only 2 are hooked up.the fan was runing all the time so i switched wires,now it cycles,but to much.the fan runs on high,i do not see a control to make it run any lower,mabe something is missing. tks tommy