Thursday, May 17, 2012
One of the problems with knowing a lot about possible complex issues is that we tend to look for complex solutions to simple problems. After learning how to measure superheat and adjust expansion valves, we send to see every problem as a problem with the TEV. This is similar to buying a car that you swore you never saw on the road before, and then by next week you notice every other car seems to look like yours. Our brains have a kind of data pre-fetch routine that tries to speed up our recognition of our surroundings that leads us to jump to conclusions. It is just how we are wired. Recognizing this, we need a system to prevent us from confusing ourselves by making incorrect assumptions based on very limited input. This is one of the reasons that systematic troubleshooting saves time in the long run. Having a system helps us avoid the temptation to solve the problem by guessing. Although there are many ways to approach a problem, I try to remember to check easy things first. If you are going to run down a list of things to check first, at least make sure the list includes simple things that don’t take long to check and should normally be checked anyway. For example, it is never wrong to check the air filter. You really should always do this anyway, and trying to check the system operation with a dirty air filter just wastes time. Dirty air filters reduce the airflow, causing a host of other problems such as low superheat, floodback to the compressor, furnaces cycling on the limit, burned heat strips, and generally poor heating and cooling performance. Similarly, it never hurts to take a look at the condenser coil to make sure it is clean. Dirty condenser coils can lead to units tripping on high pressure switches and compressor internal overloads opening. Always check to see that the thermostat is actually set to bring the unit on. Don’t assume that the thermostat is set correctly. Customers often don’t know how to set their thermostats, especially with the newer electronic thermostats. If the thermostat uses batteries, a fresh set of batteries will often cure a thermostat that is acting erratically. While you are at the thermostat, set the fan switch to on. If the fan comes on, you know that you have power to the indoor unit and also control voltage. With digital thermostats that have batteries, seeing a display on the thermostat does not necessarily mean you have control voltage because the display can operate from the batteries alone. If a unit will not operate, you need to check power to the unit first, and then check control voltage. The problem will often become apparent during these initial checks. Even if the problem is not discovered during these preliminary observations, you have eliminated many common problems in a relatively short period of time.