Unfortunately the advice about the drier switch will be wrong 90% or more of the time. I almost never see a bad switch. The problem invaribly is that the AC is running at a reduced pressure either due to low charge or other mechanical issue.

The low speed fan doesn't come on till a high side pressure of about 295psi occurs. On a full system and a hot day that occurs before the engine is hot, but on a cool day it may never occur and if low on charge it won't occur either.

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