Coleman gas furnace model #8665d766,..the burner cycles great,...but fan motor will sometimes continue to run,..if you hit it on the front side lightly,..it shuts off...?

When you say the the furnace re-starts 8 times before shut down, what is cycling 8 times? just the indoor blower or is the main burner re-firing 8 times? If it's only the fan it sounds like the fan control.

There should not be a pilot on a direct vent furnace. When you turn up the thermostat for heat the 1st thing to happen is a venter motor should start, it should vent for approximately 45 seconds, the air switch will verify a vacuum in the burner box, then a spark igniter should start clicking to start the pilot, then the flame rod will verify the pilot, the igniter will stop clicking, and the main burner will ignite and remain on until the thermostat has satisfied the set point. These guideline steps must be satisfied before the controller advances to the next step. The 1st step is the venter motor running, sometimes the motor will stick over the summer months, spin it manually to unstick it. PS, nothing runs if the fan door cover is open, as that shuts down the power to the whole furnace.

There are 2 types of burners. Atmospheric (or ribbon) type & inshot. I would imagine yours are Atmospheric...the longer type burners that protrude into the heat exchanger if they are corroding. Which also means you have an older furnace. Condensation can occur if there is not enough removal of flue gas...or... water is getting down into the burner from the flue. Have someone check the draft pressure to see if it has a proper draw when running. Coleman Evcon also made a furnace that is called a blendaire system. This system has a lower control board @ the furnace & and upper control board in a fan on the roof. The purpose of the fan was to blend air into the return from outside via roof fan to introduce fresh air in a tightly enveloped manufactured home, along with pressurizing the attic space to help keep the attic dry. If you have this type of system, your motor may be not working on the roof. Good luck!

The booster motor? Do you mean the inducer motor that helps push the exhaust? If the inducer motor won't shut off when the thermostat is satisfied and everything else does shut off, it sounds like the contacts on the relay that powers the inducer are at fault

Flip the lower panel over and look for a wiring diagram. On that diagram there will be a diagnostic chart. Let me know what 5 blinks represent. Then I want you to read on.

On a call for heat, the 24 volt thermostat sends a signal to the control module. The control module will indicate a call for heat with a light on the control either blinking or remain solid depending upon model. The inducer (exhaust) blower will purge all gasses from the furnace and pressurize a pressure switch. Once the pressure switch tells the module to continue, the electronic ignition will energize and send 120 volts to the igniter. The igniter will glow and you will be able to see it if viewed thru the small inspection port. Once the igniter gets hot enough, it sends a signal to the module opening up the gas valve (24 volts). Either a pilot will come on or the burner tube will ignite then spread the flame to all burners. Lastly a safety sensor will be looking for a certain temperature within a few seconds and the furnace will continue to operate and the room air blower will turn on in a minute or two.

What could go wrong? The unit will not run if there is no signal from the thermostat (bad thermostat or broken wire), the control module does not sense a signal from the thermostat (bad control), the inducer does not energize (bad motor), the pressure switch does not close (blocked vent piping, bad switch, plugged condensate hose), the igniter does not energize (bad control, bad igniter), the gas valve does not open or there is no gas (bad gas valve, broken wire, no gas), the pilot does not light (dirty pilot), the burner does not light (bad burner, plugged orifice, not enough combustion air), the flame does not spread to each burner (bad flame spreader, dirty flame spreader, more bad burners), the flame safety sensor does not detect flame (dirty or bad flame spreader, bad flame sensor, broken wire, bad control), or the room air blower does not energize (bad fan motor, bad control).

That sounds pretty normal for most furnace/heater products. They run the heating element with fan for a cycle then after the heater reaches temperature it will shut off and the fan will continue to run to cool the element and to circulate the heat that it produced. If you want the manual for this product it looks like you can get it here: http://homeappliance.manualsonline.com/ex/product/headline/m/Coleman%2BEvcon/d/furnace/p/DGATO75BDC

That's the fan switch. It's a thermostat that controls the fan coming on and off, it's probably failed and needs to be replaced. You can see it if you take the front off the furnace, the wires come off it and go to the fan motor.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/craig_3fa289bf857b1a3c

make sure high voltage wiring is correct

The clicking noise is a relay or switch of some sort. You are right about that. I have 2 questions. 1) does the thermostat have a mercury bulb in it? 2) when the fan shuts off and on, does the burner stay on?