Condenser fan motors come in a couple forms. PSC style and ECM style. PSC motors are easily identified by the run capacitor that comes inside the service panel with them. ECM motors are electronically commutated motors and run on their own power. Today we're going to talk about the PSC fan motor which you'll see on a lot of the basic 10 to 14-seer single-stage systems out there. There's only a few things that can go wrong with your typical PSC motor. Voltage from the panel isn't sufficient, the contactors bad, the capacitors bad, or there's damaged parts inside the condenser fan motor. I've gotten this call before. The customer says that the outdoor unit is making a very high-pitched noise, louder than they've ever heard before. When you get to the house and turn on the AC, you walk on to the outdoor unit and you find that the compressor is pumping the refrigerant but the fan on top is not spinning. What's happening here is the condenser fan blade isn't spinning which normally removes the heat from the outdoor unit. If it doesn't, the compressor will overheat and shut down but not before putting up an excreming hissy fit. After that the internal overload switch on the compressor opens. It takes about 45 minutes or so to cool back down and then retry running again. Heats up, shuts down, cools off, restarts, and over and over. In this case you likely have good voltage to the system but just to be sure make sure that you have about 240 volts to the load side of the contactor while it's running. This lets you know that the line voltage is good and that the contactor is good in one quick test with your multimeter. You only have so much time to do this before the compressor shuts down but next I usually take a stick or something and try spinning the fan blade with it. If the fan blade starts spinning after giving it a little nudge I'd check the capacitor next. That capacitor is what helps it start and run efficiently. If the capacitor checks out good then you know that you have proper voltage getting to the motor so the condenser motor is bad. If the fan blade doesn't keep spinning after you nudge it the capacitor could be good but it's still check it. If it's good the condenser fan motor is bad because it's got power to it but it's not spinning. I've seen this happen when a big windstorm hit an area recently and knocked some of the branches down into the top of the AC. The shroud on top usually does a great job of protecting the fan blade but in this instance a stick wedged itself in there and caused the motor to burn out. Another reason this can happen especially on universal replacements is the inside of the motor got wet. These motors come with rubber plugs sometimes and those plugs have to be placed in the top side of a downward mounted fan and in the bottom side of an upward facing motor. The ports on the opposite side should remain open so that any moisture that does get into it can drain out. Happens all the time. I would say check the fan motor for a short to ground right now but the main breaker or service disconnect uses would have usually tripped by now so let's check the motor windings first to see if we have an open or damaged winding. Take the wires off the contactor and the capacitor that lead to the fan motor. You can refer to your wiring diagram that comes with the AC and check your ohms resistance between common which is the wire that's hooked up to the C on the capacitor and start. Usually the brown one but it's the one that's attached to the fan terminal on the capacitor. You should read a fairly low amount of resistance here. If you read OL on your meter then you have an open start winding. Next let's check common to run or the black wire or the only one that's connected from the contactor to the fan motor. You'll likely measure a lower amount of resistance here. If it's OL then you have an open run winding. If you have OL on both the motor's windings the motor's internal overload switch could be open. If you just allow time for it to cool down and it still won't run then go ahead and replace the condenser fan motor. Just in case you do have good windings let's go ahead and double check to make sure that the motor isn't shorted to ground. You can check this with your own meter but I usually just use the continuity setting on my meter. Check between the frame of the motor and each winding. Common start and run. Make sure that you're not using a painted surface for the frame either. You want to use a metallic base for this test. If you have continuity between any of these and the frame of the motor go ahead and replace the condenser fan motor. Well I hope this helps you to troubleshoot your next condenser fan motor. This is one of the easier components to check. 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