More heater blower questions (sorry)

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motorgnome
Confirmed BX'er
Posts: 32
Joined: Mon Dec 28, 2015 6:13 am
Location: Kincumber, NSW Australia
My Cars: BX 19 TRI, Mk1 MG Metro, Mk1 Metro VP, Triumph Dolomite Sprint, Lexus LS400
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More heater blower questions (sorry)

Post by motorgnome » Sat Sep 23, 2017 12:22 pm

Hey guys

I've got a question regarding my heater fan blower on my BX19 TRI with factory air cond.

The fan blower only operates over the last 1/3rd of the fan speed dial. It does vary speed, & the high speed kicks in when turned right around, but from about 6 o clock, back, there is no fan operation. Is this normal? I have just recently got the fan blower operational for the first time. I have cleaned the rheostat & replaced the power transistor with a MJ2955 , whilst also cleaning the earth up on the heat sink body & re-soldering all the joints. From what I understand. the power transistor varies the voltage according to the feed from the rheostat. So does that mean my rheostat is faulty, or have I fitted the wrong transistor.

Thanks, Jason

motorgnome
Confirmed BX'er
Posts: 32
Joined: Mon Dec 28, 2015 6:13 am
Location: Kincumber, NSW Australia
My Cars: BX 19 TRI, Mk1 MG Metro, Mk1 Metro VP, Triumph Dolomite Sprint, Lexus LS400
x 1

Re: More heater blower questions (sorry)

Post by motorgnome » Tue Sep 26, 2017 1:41 pm

I will answer my own question...I have fitted a wrong power transistor. I ordered a different one, from the list of suitable replacements in the FAQ section on heaters..& that has solved my problem.

Incidentally, if anyone was wondering where that earth goes, the one on the rheostat wiring that often fails & you join it with the illumination earth to restore fan operation...well, it does go to the power transistor module in the fan duct. It connects with the bi metal strip that touches the base of the transistor. The bi metal strip, when heated (by a stalled fan motor) would heat up, bend & break the earth circuit to the rheostat, cutting out power to the fan. Corrosion builds up where it touches the transistor, the earth fails, the fan doesn't work, so you give it another by splicing it with the illumination earth at the rheostat wiring.. You will lose the overheat protection, but I don't reckon it's a big deal.