how can i fix heater on piccaso xsara?

heater an air co not working on my piccaso used to work intermittingly would not work on start up but if switch was set to 1 2 3 or 4 and if i went over a speed bump the heater blower would burst in to life then wen engine turned off wouldnt work again un less hit bump then it stoped working all together had it to cittreon dealer they tell me its the ignition relay switch and will cost £300 but if its the relay would expect over things not to work ac switch does not light up when pressed demister switch next to it does light up and all dials are lit when cars lights are switched on any ideas