2001 Dodge Ram • 120,000 miles

Sometimes I get in the truck and crank it and the blower works ; sometimes it does not, usualyy when I need it the most!
I can hear the comrpessor cycling, I had a newe control unit put in a while back because I only had a high speed, now when it works I have all the speeds. I read somewhere that if you hear a ticking sound the blower is going out. I hate to buy another motor and install it and find it was not the issue. Could it be the resistor block or is that inside that control unit that was changed out. I checked the fan fuse, seems OK, swapped the fan relay with and identical one beside it, didnt seem to make a difference, Auto Zone says a loose connection and it may be, I have yet to pull the unti out and see, but I figured that you may have seen or dealt with this beforte, surely someone has. Please help. Dont mind buying the parts, just need to know which ones to buy ! Thanks to all. Dave.

June 18, 2013.

The power module would be my first suspect but since it was already replaced the next suspect would be the motor itself. Worn brushes will make intermittent contact but the clue is the motor should start working after you hit a few bumps. You can also try banging on the motor to see if that will get it started.

Measure the voltage between the two wires. If you find 0 volts, don't overlook burned contacts in the ignition switch or two overheated terminals in its connector. There was a modification to install a relay to take the high current load off part of the ignition switch but at some point that relay got incorporated into the under-hood fuse box. Look for a relay labeled "Accessory" or something like that. If you find one, switch it with another one like it.

Jun 18, 2013.
Thanks, I was afraid you would say that. I had a Ford that teh ignition switch came completely aprt due mechanical stress of the harness. They can be a problem. There is for certain a blower relay under the hood in the fuse box. I swapped another identical relay next to it with it but it had no effect.

Today I think I got a true indication though, when it started it squealed a moment. Bearing going bad. I think a new motor is the fix here. Thanks for the advice. You rock.

Jun 19, 2013.
Yeah; I rock. I have a lot of people fooled!

To be safe I would clip something to the motor connector that would allow it to remain plugged in and you can measure the voltage. If you find voltage but the motor doesn't run, that's pretty conclusive that the motor needs to be replaced.

Be aware too that when a computer module controls the motor speed it does that with "pulse width modulation". That means it turns the motor on fully, then off fully hundreds of times per second, and it varies the percentage of on-time to vary the speed. Digital voltmeters take a reading, analyze it, then display it while taking the next reading. It will see either 0 volts or 12 volts, depending on when it takes a reading, not the average voltage. For this type of test a test light is more accurate than a voltmeter.

You can do the test with just the test light connected to the two wires in the plug but that doesn't put much of a load on the power module. To say it another way, the module might have no trouble running a test light but it will fail when trying to run the motor which draws a lot higher current. That's why it's best to connect the test light AND the motor. The test light will give you the indication of whether there's voltage present and the motor will make the module work as hard as it normally needs to.

Jun 19, 2013.