Do it yourself ac repair is a bad idea.  The same goes for furnace repair, maybe even more so due to the fact that you are dealing with combustible gases and possible carbon monoxide issues.  Sorry to start with my conclusion, but I feel strongly about this.  I can't remember how many times over the last 17 years I have been called in to correct a problem that was created by someone trying to "do-it-yourself".  Or maybe they called a non-licensed person (moonlighter) to fix their ac in an effort to try and save a few bucks.  In the end, they end up paying more by having a licensed professional do it right.  I will give some examples of this. 

When I was green behind the ears (about 1 or 2 years experience), I went on a service call.  When I arrived, I found nearly all of the furnace wiring disconnected and hanging out of the furnace.  The homeowner had tried to repair the furnace himself without success.  The furnace schematics (wiring diagram) was faded and illegible.  So, I had to start from scratch and figure out how to rewire the furnace.  And, there were quite a few wires too.  It looked like a spaghetti mess lol.  I spent about 2 hours rewiring the furnace before I could even begin to diagnose the original problem.  Once I had the furnace wiring back in place, it only took a few minutes to diagnose and correct the problem.  The homeowner paid more than he would have paid if he had called in the first place instead of trying to fix it himself.

A common DIY ac repair is the thermostat.  I will admit that people have more DIY success with thermostats than other HVAC related repairs.  That said, I have gone on quite a few service calls where someone has replaced their thermostat but still had a problem.  In some cases, people assume that the cause of the ac or furnace malfunction is the thermostat when in actuality it is the furnace or ac itself.  Which means they wasted money replacing a thermostat that did not need to be replaced.  In other cases, the homeowner incorrectly installed the thermostat and created a new problem that did not exist before.  Namely, shorting out the transformer or fuse on the furnace.  And, sometimes the new thermostat itself is damaged by the incorrect wiring.  Which ends up costing more in the long run to correct.

In the summer of 2011, I went on an ac repair call.  The homeowner had paid a handyman (moonlighter) to repair his ac about a month earlier.  The moonlighter replaced the outdoor fan motor which had failed again.  During the diagnosis, I found that the motor he used was not an O.E.M. motor, but an aftermarket motor.  In some cases, an aftermarket motor can work, as long as it matches the specs of the O.E.M. motor.  O.E.M. stands for "Original Equipment Manufacturer" specifications.  But, the motor that the moonlighter installed did not match O.E.M. specs.  The capacitor size was different (not an insurmountable issue), the rotation did not match the existing fan blade (which required a new fan blade), and the biggest issue was that the O.E.M. specifications require a motor enclosure that is "totally closed", but this enclosure was "open".  The picture above is from this service call.  You can see the open enclosure.  Also, he clamped and taped the capacitor to the side of the motor instead of installing the capacitor in the control box where it belongs.  Long story short, I had to replace the motor, the dual-run capacitor, and the fan blade all with O.E.M. parts to repair this.  The home owner paid more for my repair because replacing the fan blade is usually not necessary for this type of repair plus whatever he paid the handyman to repair it the first time.

Another example illustrates the necessity of having a competent professional service your furnace and/or ac.  Several years ago, I went on a furnace repair call for a tenant property.  The landlord had a "maintenance" guy try to fix it before calling us.  I found that the furnace "flame roll-out safety" had been by-passed.  Right now, all HVAC professionals reading this are gasping!  You never, ever by-pass safety controls.  They serve a vital role.....SAFETY!  A furnace running with a by-passed "flame roll-out safety" poses a fire hazzard.  When safety controls fail, it is usually when they are detecting the condition that they are designed to prevent.  Which is the worst time to by-pass the safety control.  It is critical in this situation to get at the root cause unlying the problem.   In this case, the furnace had a defective heat exchanger causing the flame roll-out condition. 

I have many more examples, plus some I'm sure I have forgotten, but I think the point has been made.  Always hire a licensed, bonded, and insured professional to service your furnace and/or ac.  It can save you time, money, headaches, and maybe your life!

Thanks,

Jim Harless