Blower motor on its way out?

[Jimmy9190]

This question is about my 2001 Dodge Dakota, 3.9 V6, manual 5-speed with about 150,300 miles on it. Week before last I went on a trip about 45 miles out of town, mostly all highway driving. I had the A/C on cold, blower fan on high speed. When I got to my destination and stopped at a red light, I noticed my A/C blower fan slowed down. I made my turn at the light, RPM's went up, and the fan speed/output went back up to normal. Came to a stop sign, fan slowed back down again. I have a voltmeter in my dash, I saw no odd or abnormal voltage fluctuations or low voltage readings. My battery is in good shape, it's a Duralast Gold and is not even 3 years old yet. My truck is in great electric and mechanical shape and runs very well for its age.

I have not driven my truck very much since that trip but the blower motor problem is still present when I do drive it. At normal driving speeds the blower works fine, if I stop at a light or stop sign the fan speed and output slow down by about 30 to 40%. I think this is a sign my blower motor is about to quit working altogether.

I guess I should also say this the original factory-installed OEM Mopar blower motor that I have on my truck. I already replaced the blower motor resistor pack about a year ago. When that happened, I still had all 4 fan speeds, but the lowest and next speeds were a bit slow to kick on when I turned the knob. It would take a few seconds to get any output at all from the AC or defroster if the system was off and I only turned it to low or the next highest speed. In other words if the system was completely off and I turned the fan knob only to the first or second fan speed, there was a pause of about 10 seconds with no air output at all, then the system would have normal air flow. I bought a new resistor pack at AAP (I know it is not OEM Mopar but the parts both look exactly the same and AAP is right up the street), swapped it out and that fixed the slow fan speed problem right away.

Thanks for any help here.

 

[AandPDan]

Don't trust the voltmeter on the dash. Hook up a digital meter and check the voltage. Odds are the voltage is dropping when you are at a stop. It's normal, to a point, when you have a heavy load on the system for this to happen.

Alternators don't put out a lot of power at idle.

Or, try it at night with the a/c on. I'll bet your headlights dim a bit at idle.

Check for a loose or slipping belt and if that's good, maybe a bad ground. It still could be the battery going too.

 

[yonyon]

An 01 Chrysler? The PCM probably controls the alternator with a PWM signal. It uses a number of factors to control alternator output to balance fuel economy, available power, and battery life. Just after starting the engine, at idle, and under hard acceleration the PCM is likely to command a low alternator output. This can give you a low battery voltage under these operating conditions and it is perfectly normal for the blower to spin slower when the voltage is down. Nothing to worry about at all.

 

[NateDN10]

This happens with both of our cars. My guess, like AandPDan's, is that your dash voltmeter is smoothing over irregularities, and if you used a standalone DVM, you'd see it dip. I say nothing to worry about.

 

[Jimmy9190]

Thanks for the replies. I have not had much time to check the system yet, but I will check the alternator, battery, blower fan motor and the rest of the electrical system today or tomorrow. I have a clamp style ammeter and a very good but old Fluke volt meter and I hope to figure out what is going on. The truck has never had any electrical problems before, and my A/C fan has never had the speed up-slow down based on RPM issue before, either. I have owned the truck for 6 years and the fan speed has always been steady and constant no matter what the RPM might be. I guess if the alternator were having problems, maybe it is getting weak but can still run the truck at speed but it slows down its output at idle, so therefore the blower fan motor slows down. The blower fan motor is rated at a maximum 40 amps of current draw.

 

[mechtech2]

Sounds normal.

 

[Jimmy9190]

Just an update here.. My blower motor worked OK over the summer. Dodge blower motors are not exactly known for moving tons of air anyway. It still had the problem with blower speed varying according to engine RPM, but it was very intermittent, did not happen all the time, so I left it alone.

This past Saturday the problem got so bad it would even drop the blower motor speed when I hit the clutch while shifting gears. When I was back in a gear and on the gas again the blower motor would speed back up. Then on Saturday night the blower motor speed was almost non-existent. I had very little air flow from the vents on any speed. High speed moved some air but not near the normal amount. Yesterday I did some testing on the blower motor, it was only drawing about 13 amps of current on high speed. I don't know for sure if that is normal, but it does not seem normal to me, especially when normal current draw for a blower motor on high speed is somewhere around 17 or 18 amps and the blower motor circuit is rated at 40 amps maximum.

Yesterday I bought a new blower motor and resistor pack at AAP, used the CCABIN discount code and saved $40.00. I replaced both parts and now the blower motor speed is much, much better. The fan moves so much more air now that it will move my hair on the third and fourth fan speeds. I replaced the resistor even though the old one may have been OK. I did a lot of research and found that bad blower motors cause the resistor pack to go bad. The resistor was only $17.00 anyway so it was cheap insurance to be sure I did the job completely and correctly. My blower fan works great now, just like a new truck.

Sorry for dredging up an old post but I just wanted to update this post, in case it might help someone else with a similar problem. Incidentally, I checked the AZ web site and the blower motor I got from AAP has the exact same part number as the one from AZ. The box says "Factory Air, made by Four Seasons". Four Seasons is a Napa supplier too, but I did not check their price on the blower motor. I bet all 3 stores sell the exact same part and I saved $40.00 on mine.