Climate Control Unit

[carday]

About 2 years ago the air con compressor stopped working so had it replaced, then about 6 months later the alternator packed up so had that replaced, however when the car came back the air con did not work Mr T said that it was the climate control unit that was faulty and as they wanted £800 + Vat to replace I decided to go without it. Anyhow recently I sourced a second hand unit from a car that had been written off, after fitting the unit to my car I naturally thought that the air con would work again, unfortunately not, was told that the unit needs to be programmed to the car, is this true and if so would that explain why the air con compressor still doesn't work ???