The a/c does not switch from cold to hot. With outside temp around 20 degrees Celsius, I raise the inside temp to 28 dC and nothing happens. Same if I lower the temp inside the car. Any ideas anyone?

 

Make sure that there is no leaks in your cooling system. I had a small leak and the air in the system prevented the heater core from circulating warm coolant. I repaired a leaky coolant hose and added coolant and the heater worked again.

 

There should be a little actuator arm with a cable on the front side of the driver firewall right behind the intake manifold that under normal conditions switches the inside temp from hot to cold but now being that these cars are alittle aged that cable operated motor burns out. U should be able to adjust the cable manually from hot to cold. Hope this helps.