My 1991 Vanagon Westfalia Camper has a 4-position fan speed selector for
the air conditioner. The 2.1l engine is stock, but the air conditioner
compressor was replaced years ago with one compatible with R-134a. In
November I replaced the condenser and pulled a vacuum on the system for
five days. Then I disconnected the A/C gauge set and vacuum pump. Last week
I took my Vanagon to a local air conditioner repair shop. They charged the
system and added oil. The air conditioner cools well, but I discovered on
Monday before sunrise that my only working fan speed is 4. All four fan
speeds worked prior to November of last year when I stopped using the air
conditioner. Should I take it back to the shop to ask them about the fan
speed selector or try to identify the cause of the problem and repair it?
Any suggestions on where to begin the troubleshooting?

Thanks,
Ryan