Blower motor resistor

Helping a friend with his 2002 Dodge Ram 3500 van (engine unknown, but I think it doesn’t matter). Blower operate only at highest speed setting. OK, that’s the classic symptom of a failed resistor. Replacements are readily available at chain parts stores.

  1. Where is the resistor located? This video shows me for a 2002 Ram 1500 van. Will it be the same on the 3500?
  2. I’ve learned here that sometimes resistor failure results from bearings going bad in the blower, causing excessive current draw. Is there a way to test that other than with an ammeter? What’s the correct current?
    2a. If the blower motor is going bad, is that something we’ll be able to replace ourselves? (Yes, I should tell them to get a Haynes or Chilton.) I don’t like the idea of taking off dashboard panels.
    2b. Is there any other “prime cause” I should look for if the blower motor seems OK?
  3. Are there any other parts (other than the switch) whose failure would also give that symptom?
  1. Forgot to mention that I have not had a chance to look at the car yet.
  2. Never mind Question 2a. I think I found the answer That also indicates that I’ll find the resistor there, too.

First, change the resistor. You will see the broken parts. They break just like light bulb filaments.
If you see no broken loops you can start wondering about other causes.

It’s due for a resistor change. 2002 is old enough for it to happen. You “have to be there” to check for bad bearings on the blower motor. If the motor is easy to remove you will be tempted to remove it. If it’s difficult, you won’t be. Deal with future problems when they occur. There are many “what ifs” that don’t usually complicate an easy fix.

The resistor block is located in the supply side plenum because it takes advantage of the air flow for cooling. Aside from excessive current, if the air flow is restricted, the block will overheat and fail. Check that the inlet filter isn’t plugged or that leaves have not accumulated and cut off the inlet supply.

A resistor usually fails due to a blower motor pulling too much current. The resistor is the symptom rather than a cause of the problem.

The blower motor current can be checked with an ammeter and the blower can be faulty with no apparent symptoms. I cannot tell you the exact amount of excess current on a blower on this vehicle as there are variables nor can I tell you the specifics on changing one out as I’ve never done this particular job on a Ram van.

Generally speaking the blowers are not that hard to change and require removal of the passenger side knee panel and glove box. Not a big deal.
As to current draw, a rough guess might be 12-15 amps on the HIGH setting. Getting 20 or more points to a dragging blower. Over time a dragging blower can also start melting or distorting wire connectors; usually at the blower connector.


Talked to the owner a little while ago. (My initial info was from his son.) Resistor was changed last September, and the fixer said that if it went out again they’d need a new blower. Aha!

Nonetheless, I’ll check for the other things.

That is the hidden information that pops up because of your “due diligence”. Good work!

Since the resistor was changed, then blew soon again, this could indeed indicate something is wrong on the blower side. However it could just be leaves or other debris in the air ducts, or in the cage. How do those fresh air vents under the windshield on the outside of the car look? A lot of debris in them? If so, get out the shop vac and clean them out so the air can flow freely. Next step is probably to remove the blower motor and determine if the motor and cage turns freely. It’s possible too that everything turns ok, but there’s a short in the motor coil, which will cause it to draw too much current. You’d have to know the spec though to determine if this is the case. You could try the smell test. If you smell a strong burned odor in the area of the motor windings, that’s a clue the coil is damaged and the motor needed to be replaced.