So... if the low speed works when you jump the pig tails then your problem is that you don't have enough pressure to turn the switch on. Unless you are in Aruba right now I wouldn't think you would see the 290psi or so that it takes to turn the fan on. Verify it with a pressure gauge on the high side. A slightly low charge will also cause this. It doesn't take a very capable AC to make cold air when its 75 or lower outside.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician