Another long, humid summer is upon us here in the DELMARVA area, and we want to pass along the three most common no-cooling issues we'll see this season. Most HVAC equipment malfunctions around the fifth year of usage are due to electrical component failures. Although there are several things that can wear out in a hard-working HVAC system, the three most common failures include components typically found in the outside condensing unit: #1) run capacitors, #2) contactors, and #3) condensing unit fan motors.
Run capacitor failures usually result in the system running but not cooling. This is because the compressor lacks the starting “boost” the capacitor provides to get it running; therefore, the heat exchange that would provide cooling isn’t happening and the unit is recirculating air over warm evaporator coils. Run capacitors are like light bulbs, they eventually go out in much the same way (with no warning and just when they’re needed the most!)… The replacement capacitor can’t be bought just anywhere—only HVAC supply houses stock them locally (and they’re not open when the thing is going to go out), so your best bet is to get ahead of this and have a replacement on hand as a spare. You can also order them online @ Grainger, etc. The replacement is relatively easy and safe, as long as you are somewhat mechanically inclined, know how to electrically isolate the unit prior to removing anything, and remember to discharge the capacitor before handling it (it has a nasty habit of “jolting” you if you don’t). Of course, having someone else swap it out is also an option, but several YouTube videos can give you step-by-step instructions if you want to give it a try.
The contactor relays are much like the old “points” we used to swap out of distributor caps when we did tune ups on our cars back in the day. Just like those, the surfaces of the contacts can become pitted and worn such that they no longer complete the connection needed to run the unit, or, they can “weld” themselves together and the unit won’t stop running. Again, this type of part failure can occur with no warning and usually results in having a unit that won’t come on or that won’t stop running. Same advice as before regarding having a spare on hand and/or swapping it out. I’d only add that not all systems still use these, some have upgraded to control boards and that’s going to take an HVAC professional to address in most cases. If you have the older system design, you might as well swap this part out when you’re changing the capacitor (or vice versa), since they typically go out around the same time.
Condensing unit fans are on top of most units and they frequently fail due to loss of lubricant and overheating (they are sealed units and there’s no way to add lubricant once the seal around the shaft starts going). The symptom is simply that the compressor is making noise/running, but the fan on top the unit isn’t spinning. This type of failure can give you warning first, as the fan may be dying a slow death and making lots of weird noises along its final journey. If you hear it making any screeching type noises, get it addressed as soon as possible. If it stops working altogether, turn the unit completely off at the breaker panel and call for service (the compressor may burn out if you don’t and the already costly repair will turn into an even costlier system replacement). The fan swap out is more complicated and challenging than the replacement of the other two parts, and since the removal/salvage of the blades is required in most cases, it should probably be done by an HVAC technician.