Why your old A/C might be intermittently cooling and what to do about it

You might notice that your air conditioner works great sometimes and then intermittently it seems to just circulate the air. Then you turn off the a/c and the next day its working again. There's a good chance your compressor is struggling to start up, but why? Is this an indication that the end is near? And what if anything can be done about it?

I have good news for you, chances are I can resolve this issue for you but first let me explain what is happening. Most older units use a reciprocating compressor(vs a scroll compressor common on newer units) . You can tell by looking at it because its Not a perfect tall cylinder unlike the scroll compressors. (Reciprocating Compressor below)

The Problem

When you turn on the A/C the evaporator coil will be under a very low pressure and the outside condensing coil will be under a high pressure. When the temperature is met the system will turn off and the pressures will slowly equalize. The hotter it is the less time it will take for the A/C to turn back on and if the pressures haven't equalized then the compressor may fail to come back on. When this happens the compressor will often overheat tripping an internal thermal switch to the motor windings from burning up. When this happens The Condensing unit fan will still run but the compressor will be silent. It may take over an hour for the compressor to cool down before the thermal switch closes and the compressor turns back on. Sometimes this will happen multiple times a day and you may not even notice it because eventually it comes back on. This is extremely hard on the compressor and may lead to premature failure.

The solution

Most likely your compressor is just using a run capacitor and is missing an optional part called a start capacitor. Think of it like a run capacitor being like starting your car in second gear going up hill. The engine might stall and shut off. So the Start capacitor is like having a first gear just as that would help a car start moving even if you are parked at an incline. The start capacitor typically gives the compressor 500% more torque on startup helping it overcome pressure differences. This part can breathe new life into older units and extend the life by years.


Hope this all makes sense and if you'd like more info please call us at 916-671-5542


For do it yourself A/C maintenance tips check out this link https://www.sierraaire.com/a-c-maintanance-you-can-do