My first thoughts was the electronic thermostat, which was not the problem as the original (standard mercury analog) thermostat duplicated the problem for a test.
The problem seems to be with a power relay that is controlled by one of the wires from the thermostat and a neutral wire. My guess is the contacts for the high current relay are burned out. Several years ago I measured the fan draw at about 10 or 11 amps. (borrowed a clip around amp meter.)
-Is this relay a common DIY part readily available at a BORG, or does each maker of forced air furnace use a unique relay?
-Is this relay sold only to Mechanical contractors?
-Will I be on a hopeless search for finding a replacement part for a 30 year old furnace?
With the cost of gas for my car, I really cannot afford the cost of replacing the furnace and central A/C.
Please help me NOT to buy a new Furnace right now.
Phil