In Surprise, near West Georgia Drive and North 149th Drive performing Fall preventative maintenance on a Trane split system. Upon arrival, cycled unit into heating mode. Replaced intake filter. Took temperature reading from supply and return. At furnace, cleaned and tightened electrical connections. Took volt and amp draws. Checked all safety switches and pressure switches. Also inspected gas supply line and flue piping. Upon departure, unit is working properly and within manufacturer specifications. Highly recommend duct cleaning and new return grill due to hooks not being secured.