HVAC Failure

[thejack]

Hi gents,
I'm an Italian boxster owner and I'm experiencing a faulty ac climate control since the car has been serviced at a porsche dealer.
So, let's start from the beginning and let me apologize for my English which isn't as good enough.
My 97 986 has been serviced at 153000km, it got new clutch, new RMS, water pump and a check at the IMS bearing plus oil, filters and other small stuff.
When I picked the car up from the dealer I noticed that the ac compressor was not running as it was supposed to do. I tried to turn it on by hitting the button and the only thing that happend was the ice icon on the lcd that lighted up. But when I released the button, the ice icon turned off immediately.
Dealer told me that the head unit must be replaced. But he didn't do any kind of dyagnose to state it. I asked him if any action done aorund the engine could have caused some problem but he assured he didn't cause the problem. To show me he was right he just brought another head unit from a 996 and connected to mine showing the ac running smooth.
It happens, randomly, that when I crank up the engine the head unit seem to work for a while then it stops, without any chance to turn it up again.
Someone experienced something similar?
I have another head unit coming from a 1996 Audi A3 with hella code 5HB 007 608 00. My original one has code 5HB 007 691 00. Anyone knows if they are compatible?
Thanks all for helping.