I have a 1999 Octavia SLXi TDi 1.9 (110BHP). When I press the air conditioner push button switch, the compressor and indicator light (illuminating the switch) only come on when the heater blower fan control is set at position 1 and not at any other position.

When the heater blower fan switch wiring connector is disconnected, the air conditioner switch does not work at all. This suggests that the controls interact but I cannot find any direct electrical link in the heater/aircon switch housing itself, so it must be somewhere else in the wiring loom.

Unfortunately my Haynes manual does not include a wiring diagram for the air conditioning circuit.

Does anyone know how the circuit is wired and can they suggest how to correct the fault or what may be causing it?

Got a picture of your control panel? Just trying to identify what system you have.

It's in pieces at the moment.

It's pretty basic. There are two large black mechanical k nobs: one on the left to control the mix of hot/cold air (which is connected to a single control cable behind) and one on the right to control the vents (connected to two control cables behind).

In the middle is a smaller k nob with four heater fan speed settings and underneath are two buttons, the lefthand turns the air conditioner on/off and the righthand is the air recirculation on/off.

Does that help?

I have the answer. The switches are all fine - I stripped them out and tested them (by the way, taking out and putting back the heater controls through the hole in the fascia is a very fiddly job).

In addition to the air conditioner only working on fan setting 1 (and not on 2, 3, 4), I noticed that the heater fan doesn't work on setting 1, but only on 2, 3, 4. This at first sight seems non-sensical, but when I measured the resistances of the heater fan motor resistors, I found all measured about 1 Ohm, apart from the resistor for speed 1, which is open circuit, i.e. burn out.

If the air conditioning eletromagnetic clutch is connected to the heater fan switch at position 1, then it would only work at 1, and not at 2, 3 or 4. This is because the three heater speed resistors are in series and if the first resistor is burnt, it breaks the connection from the 12 v supply through the chain of resistors to the clutch.

Replacing the resistor should solve the problem. I confirmed this by shorting the resistor terminals with a screwdriver, which causes the air conditioner clutch to cut back in.

My local Skoda service agent has quoted