My heater / air conditioner blower motor seems to be flaking out on me. It works perfectly when I first start the car, then after about 5 minutes, it slows down to practically nothing and makes a noise. I thought for sure that it was the blower motor, but now I'm having second thoughts. Could the motor be overheating due to something being clogged? Could it be a problem with the fan speed control?

 

How does the HVAC filter look? Is it totally clogged? What happens if you put the system on "recirc". This should bypass the filter if that's where the clog is. If recirc doesn't do anything, then it's possible that enough debris got past the filter (poorly installed?) to gum up the fan. It's also possible that the fan motor ground is in need of inspection (corrosion?). Could also be the switch too.

 

I haven't ever checked the filter.

 

Might be time. There could be 1/2 a bird stuck in there.

 

It could also be the blower motor's transistor flaking out when it heats up, or a blower motor going bad. You'd need a Meter to check the volts to the motor when the speed slows down.

 

Don't forget to mention that your car took a cold shower with the top down the other day. Was this problem occurring before that?

 

A cold shower for the car isn't good for electrical contacts. You may want to take a look to see if there is any H20 in the connectors.

 

I pulled the blower out today. There isn't any indication of water damage. I also used my "professional engineering intuition" to determine if it would be possible for a slow water "leak" to damage it ... I don't think it could. The motor is sealed up pretty well, and the fan blade is a huge umbrella above it.

What is extremely weird is that the fan blows like a friggin' hurricane if I turn it upside down, then starts jolting and slows down to a crawl when I turn it upright. Does this make any since? Why would the angular orientation have an effect on its speed? Does anyone have a suggestion?

 

As a educated guess, It sounds like one of the motor bearings are damaged. When you turn it upside down the load is taken off the bearing and it can spin freely.

 

Could also be motor brushes.