# problem cab heater control



## vivallan (Aug 19, 2013)

Hi everyone.
 I  own a 1992 hymer B534 import based on a fiat ducato with a 2.5 td engine. Since owning this vehicle the cab heater switch has never worked, "someone had wired up a switch so blower would work at full speed" I have in the last few days decided to see if I could fix this problem by replacing the heater blower resistor. Alas this was not the problem. There has been fitted at some point a type of resistor between the wiring loom for the blower and the switch which I have found to be burnt out, however I have searched online to see if I could identify this burned out "resistor" to no avail. I now find myself posting pictures on different web sites to see if any one of you experts can identify this part. here's hoping.Photo's attached.
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## maingate (Aug 22, 2013)

Have they not rigged up a new 12 volt supply when they did the bodge on the fan. If a resistor is refitted then it should work as normal. Try asking the question on the Fiat Forum.


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## Deleted member 27096 (Aug 22, 2013)

I can tell you that the resistor box is not a standard fitting.

You need to get a replacement harness from Fiat or if there is enough wire join using proper crimped connectors.


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## Smaug (Aug 22, 2013)

I am reading between the lines here so please correct me if I am wrong while I try to diagnose the problem;

I am assuming the heater is OK but fault is that the fan is either full on or off.

The usual (simple) way of getting different fan speeds is to have a parallel set of different resistors in line with the fan so that each allows a different speed as you switch from one to the other. The burnt out component looks as tho it may have been such a resistor set with different leads connected to a switch for different speeds. 

If you can find a Ducato wiring diagram it MAY (but probably not) tell you what those resistor values were so that you could rebuild the burnt out box. Alternatively, get a second hand unit of a scrap van & try that. Or you could just try a random selection of resistors to see what speeds you get & select a few suitable settings. 

Resistors are cheap from specialist shops, but make sure you tell them what you are trying to do so that they can make sure you have something robust enough that won't burst into flames next time!


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## Smaug (Aug 22, 2013)

A mechanical rheostat may be hard to find these days, especially one capable of taking that sort of current (5 amps ish?) Pity there are no old radio shops around, do Radiospares still do online parts?

I see there is a RS Components web site, but no rheostats listed. But 3 or 4 discrete speeds is normal for most vehicles these days.

There are high power rheostats but they are very dear.


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## Smaug (Aug 22, 2013)

Sounds like a carbon track resistor then. There is a high resistance carbon track across the 12 supply & as you rotate the almost frictionless contact across the track the voltage offered to the motor increases & decreases.


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## vivallan (Aug 23, 2013)

*Thanks*

Thanks everyone for your reply's.
 On further investigation i have found the original part of the loom hanging down behind an air con unit that is fitted. i have connected the original cable from the blower motor to the loom that i found and everything seems to be working as it should. i can only presume that because of the air con unit obscuring the original heater blower  resister pack that someone has fitted this extra resister pack to save taking out the air con unit.

Thanks once again everyone for your reply's,helpful as ever.


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## Tbear (Aug 23, 2013)

Hi Smaug,

I think you will find that if you give RS a ring, they will put a very knowledgeable chap on the other end of the line. They may not want to sell you a 10p resistor but will be happy to sell you a specialist part such as a Carbon Track Resistor.

I have no connection with them but have made a few purchases from them over the years.

Richard


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