Arrived on site to preform a 20 point maintenance inspection on a ac pro furnace. Upon arrival unit was running, took a inducer amp draw inducer motor was in range. Checked the flue vent and gas piping for leaks, there were no leaks detected at the time of maintenance. Checked all safety and limit switches, they were functional and operational. Took a static pressure test static was a little high but when I changed filter it went back down to normal ranges. Condensate drains were flushed and drained at the time of maintenance. Recommend to the customer about surge protection, hey wanted to talk that over and might consider it next visit. Unit was operating upon departure.