Most furnaces use a preset, adjustable, time delay circuit to control the start of the blower motor. Some higher end models may use a temperature sensor to determine when the blower should come on, but this is a less common setup. It's possible that something in the furnace is broken and/or configured incorrectly, but it's more likely that the thermostat has been installed incorrectly.
A thermostat in its most basic form, is simply one or more thermally activated switches. In the olden days, it was likely a mercury switch, that only controlled a heater. Most more modern thermostats control heat, A/C, and the blower fan. In your case; since you're having trouble with the fan, we'll focus mostly on the fan settings.
A typical thermostat will only have two settings for the fan, ON, or AUTO. In the ON position, the fan will run continuously. In the AUTO position, control of the fan is handled by the furnace instead of the thermostat. Since your fan does not run continuously, I'll assume you have the fan control on the thermostat set to AUTO.
If you accidentally connected the FAN wire to the HEAT terminal and/or the HEAT wire, every time the thermostat called for heat the fan would immediately turn on. Since this is the easiest, cheapest fix. I'd start by making sure the thermostat is wired properly.
Well, I know this post is old but a simple way to test your pressure switch is to turn off your furnace first and close the gas valve for safety, then gently unhook the air tubing from your draft inducer and gently suck on it using just the suction your mouth creates, I wouldn't inhale it, you should hear the pressure switch click and feel a restriction while sucking on it. If you do not hear a click, can keep pulling air, or cannot pull any air at all your pressure switch is probably bad. If your pressure switch tests good, then try cleaning out the inducer connector it could have junk in it. If it does have junk in it, it may be a good idea to change it out because it is probably rust. That is what was wrong with mine. I had a faulty pressure switch and s rusted out inducer fan. The inducer motor itself ran fine. After changing out the pressure switch it still would not fire up. So i pulled off inducer motor and the fan was completely rusted out.
Best Answer
No, that sounds like it's running correctly. If you want to adjust the timing, you can install an On Delay Timer on your circulation fan. You can use the ICM251 Fan Blower Control - Dual On/Off Delay Timer. It has an Adjustable Time Delay, and a 20 amp 120 volt relay built in. The On delay lets air reach proper level prior to energizing fan, and the off delay purges ducts of residual air to increase efficiency.