Hot and steamy cruiser - A/C MacIver repair (advice) 105 series


New Member
Dec 23, 2016
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Hi guys can I get your thoughts on something?

So my car a/c doesn't work. and well.. its getting hot in Australia and im leaving in a week for a long road trip into even hotter regions. I took it to the mechanic and they said they couldn't work it out but all the sensors are good its gassed up fuses/relays are fine. "must be something to do with the body control unit" So. I pulled that apart cleaned all the dust and crap out, still nothing. Took it to an auto elec they said similar thing but couldn't guarantee changing the dash control unit would fix it. Plus they are also hard to match/find and expensive.

(A/C button on the dash is completely dead, no light or anything)

There is basically just an electromagnetic clutch on the compressor. I shorted that to the +12 and it engaged and worked perfectly. Started getting cold air from the air con.

Soooo.... What I'm thinking.... I bought a timing relay from jaycar I can set the on/off interval (ie 2 min on 2min off) I'm planning to bypass the controls and engage the clutch with this relay.

This bypasses any sensor control (compression and temperature) on a scale from 1-10 how bad of an idea do you think this is?

Simple in theory
Dash switch> ACC relay > timing relay > clutch.

Am I setting myself up for a RUD ("rapid unplanned disassembly" - Elon musk)?

Last edited:


Well-Known Member
Apr 6, 2010
Yeah, that will work. If its low humidity out you wont need the off too be too long, only long enough to let the evaporator defrost.


Well-Known Member
Oct 7, 2014
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Just wire the compressor through the low pressure switch. Hopefully you have a switch not just a sensor. Also take a feed from your fan to ensure the fan is running for the AC to run. Wiring the engine over temp cut out is also a good idea.
Reasons being:-
1, your system could run on a vacuum which is not good as any leaks could pull in air.
2, if your system loses all refrigerant, the compressor will still run and could potentially seize up due to lack of oil carried round the system.
3, without the engine overtemp cutout, on a really hot day (which I hear you get in Oz) the engine could overheat due to the extra heat in front of the radiator generated by the AC condenser.
4, with the LP switch in circuit your system will run as normal.

I'm not entirely convinced by the diagnosis you have been given. There's plenty of reasons why the controller could be holding the AC off as shown above.

If you can get hold of a wiring diagram (maybe a member here can help with that) things will become clearer.

Fan running and signal from this present at controller
LP switch closed
System full of gas (how do you know it is full?) this is the number 1 cause of AC failure and the sight glass will look the same full or empty, gauges need attaching to system.
Engine overtemp switch closed.
Check for damaged wiring or poor connections, particularly around sensors.
Revisit the refrigerant level, use a proper fridge engineer/mobile AC engineer.

In short, just wiring in a timer will make it work but could wind up wrecking either the compressor or overheating your engine. Removing safety controls is never a good idea. Hope this helps, good luck with it.