How to bypass heater resistor

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Mr B
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How to bypass heater resistor

Postby Mr B » Sun Apr 01, 2018 4:42 pm

Hi guy's,

Just a quick question, how exactly do you bypass the heater resistor, my heater motor has stopped working and as the motor itself is less than a year old I can only assume the resistor is toast, I have checked the fuse and associated wiring and all seems fine, this morning I ran a direct live to each of the 3 terminals on the resistor but not a peep from the motor, any suggestions other than the resistor?

Cheers

Wayne

Paul G
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Location: High Wycombe

Re: How to bypass heater resistor

Postby Paul G » Sun Apr 01, 2018 6:31 pm

Mr B wrote:Hi guy's,

Just a quick question, how exactly do you bypass the heater resistor, my heater motor has stopped working and as the motor itself is less than a year old I can only assume the resistor is toast, I have checked the fuse and associated wiring and all seems fine, this morning I ran a direct live to each of the 3 terminals on the resistor but not a peep from the motor, any suggestions other than the resistor?

Cheers

Wayne


Even with the resistor blown the fan should run on fast speed. I'd check your wiring and fuses first.

Assuming the car's a MK3 it's Fuse 5 and it's a black/red and yellow wire down to the heater box.

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Jasonmarie
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Re: How to bypass heater resistor

Postby Jasonmarie » Sun Apr 01, 2018 6:34 pm

Martin at Capri Gear does a resistor that are better then the old ones .
Ford Capri 2.0 Laser 1987 Mercury Grey ....... :beer:

Mr B
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Re: How to bypass heater resistor

Postby Mr B » Sun Apr 01, 2018 7:13 pm

Thanks for replying guy's, checked the fuse and it's fine but changed it out with another just in case, I ran a 12 volt wire directly to each of the resistor terminals but no joy, the heater motor has been getting progressively slower over the last few weeks but had none of the usual chirping, squeaking or groaning so I assumed, perhaps naively, that the motor itself must be fine, I'm sensing a school boy error on my behalf here

Wayne

timfromull
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Re: How to bypass heater resistor

Postby timfromull » Mon Apr 02, 2018 7:12 pm

Jasonmarie wrote:Martin at Capri Gear does a resistor that are better then the old ones .

I've just bought his last one this weekend.
Does he have them made in batches?

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Re: How to bypass heater resistor

Postby Caprigear » Mon Apr 02, 2018 9:11 pm

Yes I do but I always try to keep at least one available at all times as I use quite a few in the fully refurbished heaters that I sell.
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Bug
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Re: How to bypass heater resistor

Postby Bug » Tue Apr 03, 2018 6:03 pm

The resistor is in the earth side of the circuit. Power goes in to the motor through the bullet connector. When you operate the switch you are completing the earth circuit. When you switch it to slow you are running the earth through the resistor. When you switch it to fast you bypass the resistor. So even if the resistor is knackered you should still be able to run it through the fast setting.
There are three connectors on the resistor 'board' as far as I remember?
One is the earth wire coming out of the motor. So if you run a wire from that one to earth, the motor will run. Unless it is seized.
But connecting another power line to any of those three connectors will achieve nothing, it is an earth you need.

Mr B
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Re: How to bypass heater resistor

Postby Mr B » Tue Apr 03, 2018 7:44 pm

Bug, thanks so much for explaining this, it all makes a lot more sense to me now, no wonder running a direct live to the resistor terminals had no effect! I've been reading the print off the Haynes manual electrical diagrams trying to work it out, an electrician I'm definitely not that's for sure.

Thanks again mate

Wayne

Bug
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Re: How to bypass heater resistor

Postby Bug » Wed Apr 04, 2018 6:21 pm

Mr B wrote:Bug, thanks so much for explaining this, it all makes a lot more sense to me now, no wonder running a direct live to the resistor terminals had no effect! I've been reading the print off the Haynes manual electrical diagrams trying to work it out, an electrician I'm definitely not that's for sure.

Thanks again mate

Wayne


Ha Ha, Neither am I! Aircraft engines/airframe techie by trade.
But all I do with electrics is imagine it as a fuel or hydraulic system. Flows the same way, switches for valves etc.
Though to be fair I've never banged my head on the bonnet after getting fuel on my fingers.....................wiggly-amps on the other hand hurt!

And my money is still on another seized motor by the way ;)

Mr B
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Re: How to bypass heater resistor

Postby Mr B » Wed Apr 04, 2018 10:01 pm

Hi bug, turns out the motor is fine, once I wired it up correctly the motor sprung into life, the resistor board on the other hand looks like it's broken/cracked in two or three places :crying:

Wayne

timfromull
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Re: How to bypass heater resistor

Postby timfromull » Thu Apr 05, 2018 9:29 am

By coincidence I'm refurbishing my heater at the moment with a new motor and one of Martin's new resistors.
I've found this post most useful, :cheers: boys.

Once done, it'll be bubble wrapped and stored with the rest of the booty I've been squirreling away for Project GBH :woot:

Bug
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Re: How to bypass heater resistor

Postby Bug » Thu Apr 05, 2018 5:03 pm

timfromull wrote:By coincidence I'm refurbishing my heater at the moment with a new motor and one of Martin's new resistors.
I've found this post most useful, :cheers: boys.

Once done, it'll be bubble wrapped and stored with the rest of the booty I've been squirreling away for Project GBH :woot:


Hey,
I've changed quite a few heaters in my time. Got it down to 45 minutes for a straight swap.
But I have to say that your idea of getting the heater first, then building the car around it sounds much easier. :xd:

Bug
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Re: How to bypass heater resistor

Postby Bug » Thu Apr 05, 2018 5:05 pm

Mr B wrote:Hi bug, turns out the motor is fine, once I wired it up correctly the motor sprung into life, the resistor board on the other hand looks like it's broken/cracked in two or three places :crying:

Wayne


Glad it's sorted.
Maybe just live with it, run the fan on high when you need it.
Once the car is above about 30mph I reckon the flow of air through is almost equivalent to low fan speed anyway

And bear this lesson in mind for the future. A lot of car electrics run power to the component and use the switch to earth it.

Mr B
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Re: How to bypass heater resistor

Postby Mr B » Thu Apr 05, 2018 9:36 pm

Hi bug, trust me this is a lesson learnt, although I'm curious, is there a reason why some circuits are wired up in this way?

Wayne

Bug
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Re: How to bypass heater resistor

Postby Bug » Mon Apr 09, 2018 6:19 pm

Mr B wrote:Hi bug, trust me this is a lesson learnt, although I'm curious, is there a reason why some circuits are wired up in this way?

Wayne


Not a clue I'm afraid.
I guess you could say you'd have a strong permanent live connection that won't get disturbed?
And you don't have power sitting at a switch that may go wrong?
Just grasping at straws though to be honest


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