99 Boxster to 03 Boxster S a/c problem
 

I have converted my 99 Box to 2003 Box S motor and DME. The internet doesn't recommend this because its a lot of wires and systems to merge. The internet is correct. I have resolved all the issues except one the A/C.

2003 runs off 7.8 and the 99 is 5.2.2 The 7.8 has CAN to control a/c and the 5.2.2 does not. The DME plug IV white and green wire from 7.8 DME will not provide the ground signal 85 to the a/c relay because it is not talking to the 99 a/c control unit. I can update to CAN a/c control unit but its more wires to deal with. has anyone been across this bridge before.

Thanks Casey

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I don't know if this will help or not but I have done something similar. I updated my '98 Boxster 2.5 to a '03 engine and wiring harness. Very difficult. The only part of the wiring harness I left was the '98 short piece which connect the Klimatronic to the '03 wiring harness. The blower and dampers work but no cooling. I purchased a '03 Klimatronic and connected it. It just hummed a bit and did nothing. I purchased what I thought to be a '03 A/C wiring harness which turned out to be another '98 A/C wiring harness. It causes both the '98 and '03 Klimatronic to hum and do nothing. I just purchased a '02 A/C wiring harness but have not connected it yet but will send and update. I am curious how you knew that there was a ground problem.