2004 2500 Hd Heater Blower Not Working

couch · March 19, 2009

I have replaced the heater blower resistor (OEM) twice in the past 4 months - latest OEM unit only functioned for 4 days. Wiring to the resistor is OK on has continuity to main wiring plug on passengers side of dash. All other heater control functions appear to be working properly - separate left / right control, heat vs vent vs defrost, hot vs cold, on / off, etc.

There is a post on here about a bulletin re this issue being related to a possible short / ground of the wires on a post / pillar - where exactly is the trouble spot supposed to be located?

Any help would be appreciated.

Mike

bill190 · March 21, 2009

Resistors can be measured with an ohm meter. Either they work or they don't. (Or there could be a loose connection and/or the act of replacing the resistor temporarily restores the loose connection!)

I don't have this truck and don't know what this problem is with the resistors? But I do know electronics. Could someone post a picture of this resistor?

What exactly is the problem with this resistor that it needs replacement?

bill190 · March 22, 2009

I have a bit more time now and can add a bit which might help with troubleshooting...

Electrical connections can be off or on... Or they can be "in-between"!

An in-between electrical connection is sort of like a bad or dirty connection. All the electricity is not getting through.

A "resistor" just makes an intentionally bad connection!

It is sort of like a water valve turned part way on and it is only letting a little water through. Not off, not all the way on, but in-between.

The amount of electricity a resistor will 'let through" is called "ohms". The more ohms, the less electricity that will get through.

So 1 ohm will let a lot of electricity through. 1000 ohms will let very little electricity through.

A 1 ohm resistor would be described as 1 ohm.

A 220 ohm resistor would be described as 220 ohms.

But a 1000 ohm resistor would be described as a 1k ohm resister. (k = 1,000)

So the terminology can make things a bit confusing. Luckily the resistors used in a vehicle would probably be less that 1000, that makes things easier.

So a heater might have a 2 ohm connection for slow speed. A 1 ohm connection for medium speed. And a straight through (good) connection for full speed. (I have no idea what you particular model resistor values are since I don't have the wiring diagram.)

Anyway you can test resistors with an "ohm meter". This will tell you in "how good the connection is" or how many ohms it is reading.

An ohm meter is usually included with a "multimeter" sold at auto parts stores or at hardware stores.

Here is more on how to use an ohm meter...

http://www.allaboutcircuits.com/vol_6/chpt_2/2.html

couch · March 23, 2009

I have a bit more time now and can add a bit which might help with troubleshooting...

Electrical connections can be off or on... Or they can be "in-between"!

An in-between electrical connection is sort of like a bad or dirty connection. All the electricity is not getting through.

A "resistor" just makes an intentionally bad connection!

It is sort of like a water valve turned part way on and it is only letting a little water through. Not off, not all the way on, but in-between.

The amount of electricity a resistor will 'let through" is called "ohms". The more ohms, the less electricity that will get through.

So 1 ohm will let a lot of electricity through. 1000 ohms will let very little electricity through.

A 1 ohm resistor would be described as 1 ohm.

A 220 ohm resistor would be described as 220 ohms.

But a 1000 ohm resistor would be described as a 1k ohm resister. (k = 1,000)

So the terminology can make things a bit confusing. Luckily the resistors used in a vehicle would probably be less that 1000, that makes things easier.

So a heater might have a 2 ohm connection for slow speed. A 1 ohm connection for medium speed. And a straight through (good) connection for full speed. (I have no idea what you particular model resistor values are since I don't have the wiring diagram.)

Anyway you can test resistors with an "ohm meter". This will tell you in "how good the connection is" or how many ohms it is reading.

An ohm meter is usually included with a "multimeter" sold at auto parts stores or at hardware stores.

Here is more on how to use an ohm meter...

http://www.allaboutcircuits.com/vol_6/chpt_2/2.html

The heater resistor actually has three resistors mounted. Last time the unit failed it allowed the blower to work on high speed only - only one of the resistors had failed / blown (checked with a multimeter) and when crossed out all blower settings worked fine.

Dealer replaced the unit again but indicated that if it blows again in the near future they will not replace without doing a diagnostic (truck is out of warranty - fair enough) so I would like to find out possible causes ... have checked / removed the blower and it spins freely, voltage is being supplied to the resistor plug for each of the respective speed settings, no blockage in air box, all other heater functions are working properly .... saw a post online here re a possible "chafed wire" causing similar problem but not sure where the problem area is located (under dash, firewall, electrical fuse block, etc.)?

bill190 · March 24, 2009

Well if one resistor has failed, then there is something wrong with the resistors or their connections.

Resistors come in many "flavors". They can be little tube shaped things, or rectangular, or just a piece of coiled wire.

They also come in different wattages. This is the power they are rated to carry. If too small, then the resistor can burn up!

So might just be a problem with the wattage of the resistors and a bit higher wattage is needed. Or could be a problem with a connection coming loose.

But seems to me if there is a problem with the part, installing the same part would have the same problem. I should think the part would need to be redesigned or made more sturdy?