Help Support Bigcoupe.com

Heater blower transistor failure mystery...

Post in this forum for topics relating to the interior.

Moderators: bfons, GRNSHRK, ron

Post Reply
northNH
Posts: 3
Joined: Tue Dec 12, 2017 11:29 pm
Location: New Hampshire USA

Heater blower transistor failure mystery...

Post by northNH » Sat Jun 20, 2020 2:06 am

Greetings from northern New Hampshire,
I’m stumped and hoping for some insights...

Over the 20 years I’ve enjoyed my ‘86 CSI, I have replaced the heater blower motor transistor every ~5-7 years with the regular old 3055s.
Always been straightforward, always successful without drama or unexpected surprises.

I recently took the car out of ~3 year storage, and after several weeks of normal blower operation (i.e. fan motor smooth, quiet and powerful for both variable and high speed operation), I lost variable speed control.

As I said, no big deal, BTDT. Everything else that should work does i.e. variable AC fan control, no blown fuses, etc.

So I bought two 3055s, installed one, straightforward as always.
After ~30 seconds it “blew” and fan stopped, back to pre-installation non-variable operation. Transistor did get hot, no fuses blown...

Huh? Removed/replaced the transistor, same result.

Got two higher-powered 3771s, and same results, both blew within 30 seconds.
And dammit, everything checks out correctly with the transistor once soldered to it’s heat sink prior to installation.
And not possible to connect the 3 wires to the transistor board incorrectly, even at my advanced age.

Although I haven’t measured the current draw of the motor (on high), I find it hard to imagine it’s the problem, as well-functioning as it’s always been.
It’s acting like the main power supply to the transistor is somehow grounding through the plastic blower motor case, but that ain’t possible.

Suggestions most appreciated.
9D42F778-7D0A-4101-A198-816026B40619.jpeg
9D42F778-7D0A-4101-A198-816026B40619.jpeg (801.57 KiB) Viewed 261 times
'86 635 5spd 175K Blk/blk orig paint/int
'92 MBz 300CE Sportlined 175K Blk/wine orig paint/int
'67 Volvo Amazon estate 80K LtGrn/grn orig paint/int time capsule
'62 Volvo Amazon sedan 65K Blk/red orig paint/int time capsule

One lucky guy...

User avatar
hornhospital
Platinum Member
Platinum Member
Posts: 2524
Joined: Sun Jul 11, 2010 6:46 pm
Location: Silverhill, AL

Re: Heater blower transistor failure mystery...

Post by hornhospital » Sat Jun 20, 2020 4:53 am

Pretty much has to be excessive current draw by the blower motor.
Ken Kanne
'84 633CSi "Sylvia"; '85 635CSi "Katja";'85 325e "Hazel Ann";'87 325is "Odette"; '93 325is "Elvira"; '95 M3 "Ashlyn"; '95 318is "Bebe"

User avatar
86_6series
Platinum Member
Platinum Member
Posts: 583
Joined: Mon Apr 02, 2007 10:08 pm
Location: West Nyack, NY

Re: Heater blower transistor failure mystery...

Post by 86_6series » Sat Jun 20, 2020 9:47 am

hornhospital wrote:
Sat Jun 20, 2020 4:53 am
Pretty much has to be excessive current draw by the blower motor.
+1

Pod
Platinum Member
Platinum Member
Posts: 4109
Joined: Tue Mar 16, 2010 8:32 pm
Location: usually in the barn, Kent, England.

Re: Heater blower transistor failure mystery...

Post by Pod » Sat Jun 27, 2020 12:20 am

A few drops of penetrating fluid, followed by some light oil on the blower motor bearings could work wonders.

emac
Posts: 53
Joined: Thu Feb 06, 2020 2:57 am
Location: SC

Re: Heater blower transistor failure mystery...

Post by emac » Wed Jul 01, 2020 2:45 am

I was having a fuse blow every time I turned the car on. Swapped out resistors, cleaned and lubed the fans and everything was fine....until the fuse blew again. It turned out to be the connector to the resistor under the dash. I tightened the female connectors on the plug and it has worked perfect since then. Dont ask me why a loose connection would cause the fuse to blow. No clue. I found it when I had the fan running and jiggled the connector and it popped and blew the fuse.

Just for grins, you may want to check the electrical connector.

Post Reply

Who is online

Users browsing this forum: No registered users and 13 guests