Blows cold air only. It is a Suburban SF-30 about 15 years old. Thermostat works fine, sail switch is getting current. When I turn on the thermostat, it takes time for the blower to come on, then thats it. I don't hear any click click likes it trying to light. I turn the thermostat on and off several times. All the other appliances work great. Time delay has current, can't get to the high limit switch. I could take it to the rv place, but they are expensive. Any help please.