Blower Motor Resistor

[Richouser]

I am replacing the blower motor resistor/transistor about every 4 to 5 months in my wife's 2003 V 40 wagon. Nice car and well kept, but this is a pain in the butt. I am using a 2N3055 transistor from Radio Shack. It works well for a few months and then just gives up. Is there a better part I could use that will last longer in this application?

Thanks!

[jimmy57]

Replace the blower motor that is drawing too much current and killing the resistor.

[RickHaleParker]

2N3771 - 2N3773 can handle more current and dissipate more heat.

2N3055 NPN Silicon Power transistor 60V 15A 115W TO3
2N3771 NPN Silicon Power transistor 40V 30A 150W TO3
2N3772 NPN Silicon Power transistor 60V 20A 150W TO3
2N3773 NPN Silicon Power transistor 140V 16A 150W TO3

If the 2N3055 is the original part number, you got something else going on causing excessive current draw or diminishing the thermal conductivity.

Is the 2N3055 the original part number?
Are you using thermal compound on the 2N3055?
Have you check for debris restricting the air flow or creating drag on the motor?
When was the last time you changed the cabin air filter?

[Richouser]

Hi Rick,
Thanks for the response. I have done all of this, including the Radio Shack pn replacement with info from another forum post. I do know that there is no drag on the motor, and the cabin filter was replaced last year and checked again recently. i am only able to find the pn for the complete resistor assembly 30864189, so I was going on faith for the transistor pn only from the post. What is thermal compound and how/why do I use it? And could I cause damage by trying the 2N3773? I have no problem buying the whole assembly but it seems like a great waste of money just to get the heat sink, especially if there is another problem in the system.

Thank you.

[Richouser]

OK I get it about the thermal grease. An electronics bug friend says tooth paste good if no grease available. I am trying that today since nowhere open to get the grease, and am using the last 2N3055 I have. If this doesn't work, where might I get the exact OEM specs on that transistor?

[RickHaleParker]

Found some pictures of of the Fan control module (30864189). The original transistor is a MJ802 which is a 30 amp 200W transistor, twice the current rating of the 2N3055 which is 15 Amps 115W. That most certainly could explain the frequent failures.

Whomever did the write up you placed your faith in, did not do a proper substitution evaluation. Without knowing the characteristics of the circuit, the 2N3055 is nowhere close to a adequate substitution for a MJ802. You can get a pair of MJ802 on eBay for $10.00. If you can wait for a shipment from China and buy 10pcs the price drops to ~$1.20 each.

If I where to put the time into it, I could probably identify a 2N6XXX that is more durable then the MJ802 but how many would make use of the information ... ???


Thermal compound AKA Thermal paste or Thermal Grease, it that grease like substance that was between the transistor and the heat sink. It fills the gaps, pushes out trapped air and facilitates better heat transfer. Trapped air is the second best Thermal Insulator there is. Trapped air is how the insulation in your walls work. You should clean off the old and apply new Thermal Compound whenever you change a power transistor.

[Richouser]

Thank you Rick!

[RickHaleParker]

Thank you Rick!

Eight months, how is that MJ802 holding up?

[Richouser]

Hi Rick,

Thanks for checking. I did not change it out right away (waited for the 2N3055 to fail) and it's been in for about 6 months now - so far, so good. Going into summer and the AC will get a workout so we will see. I have noticed the fan speed modulates quite a bit with this resistor, where the incorrect one was pretty constant. But I don't care if I do not have to change it out again.

[alschnertz]

Richouser;
What was your blower motor doing that initiated this repair?