How to slow the blower motor on my furnace?
You should have your furnace serviced if it has been more than two years since it was done. There are a number of things that could be happening including a defective, dirty or failing high-limit switch - which determines the maximum temperature of the heat-exchanger - which determines the temperature of the air coming out your ducts. When the system is serviced, the tech will check the limit switch, clean the firebox and check the burner (if oil, replace the nozzle and clean the filter on the oil-line), check/replace the air filter, check the fan motor and bearings and belt (if any), check the thermostat setting including the anticipator - the part that sets the high-low thresholds on the stat - and generally make sure that the system is operating at its optimum. He will adjust or replace the limit switch sensor if that is the issue.
there is a reason the blower and furnace are built together. the blower is designed to move a certain volume of air across the heating coils if you were to slow the flow down you risk overheating the the furnace. there are safeties built in to help prevent this but damage is much more likely. my guess it this is a newer furnace? if so the out put air tends to feel cooler because it might be a high efficiency model if this is an old furnace cool out put can be caused by frequent stopping and starting (hunting) look at your thermostat location
You never ever, ever want to slow down the blower speed. Leave it set by design. Are you sure its not short cycling and thats not the real problem. I suggest you call a service man to have a look for proper operation of your system. Also, verify that your return ductwork has no breaches in it or has not separated somewhere. This can cause the issue you described as your sucking on cold air form somewhere while trying to heat the air.So you get a wacky balance of heat.
The air coming from the ducts is not supposed to be hot, just warm. Don't mess with the motor speed or you may cause a fire. You will also void any warranty on the furnace.
Forget that,someone was jerking you around.