Overview

Air Conditioning System2 - How Your Air Conditioner Works

TroubleShooting

Problem	Probable Cause
Won't Start	Breaker Thermostat
Won't Start - Buzzing Sound at AC Unit	Bad Capacitor
Furnace fan not turning on	Thermostat Breaker Fuse in furnace blown (check wires at AC Unit if blown)
Water running around the outside of the furnace	Blocked ac drain

Bypass the Thermostat

With the power on, you can bypass the thermostat by pushing the plunger in to connect the 240v.

Listen for buzzing, etc...

Next check for 240 VAC on contact points.

Capacitors

Checking the Capacitor

The capacitor has a rating on it. Capacity is written as HERMS capacity + FAN capacity.

ex. 35+4uF

Measure the capacity from common to what you are measuring.

ex. Fan measurement should show 4uF and Herms should show 35uF.

Thermostat Wiring

Voltage: 24 VAC

Mark's Unit

Sears Model# 875.47270

MD: 3207-1 11A

References

Reference	URL
How Air Conditioners Work	https://servicechampions.com/how-your-air-conditioner-works/
AC Won't Start	https://www.youtube.com/watch?v=wzAA4dlp_70
AC Capacitor Fail