Volvo 760 ACC question

[Aubergine S70]

Hi, I’m looking for a little advice/ knowledge on my 1987 heater resistor/resistors. The heater blower resistor has failed. The new replacement ones I can source have a 4 spade connector. The one fitted to my car has a 5 spade connector. The spades look in the same position but 1 spade missing on the new replacement one, would the 4 spade resistor be compatible to mine? The other question I have is there’s also a separate resistor with a 2 spade connection, I’m unsure what this controls? My car is fitted with factory air conditioning and automatic climate control (ACC)

Any advice on this is greatly appreciated.

Thanks for looking

[360beast]

Has it actually failed?

Usually they get corrosion across the wires on the back of the resistor and just need this cleaning off and normal operation is resumed.

[Forrest]

I think the way these work is that there is a common output and an input for each fan position on the programmer except maximum which bypasses the resistor. Hence the 4-speed fan on a standard 740 would have three resistor taps corresponding with positions 1,2,3 on the switch. Thus the more common four pin resistor.

In theory you could leave one disconnected but it might be annoying if the ACC tried using that fan speed. Alternatively, you could fit two onto one output but I’d be wary of back-feeding voltage to the programmer that way. Maybe use diodes to avoid that problem.

Best to look at the circuit diagram and understand exactly what you’re doing.