As with any heating or cooling system, rooftop units must be regularly inspected and maintained if you want to avoid costly failures.  These systems, however, are not quite as simple as the average residential HVAC.  Most commercial and industrial properties are overseen- or regularly visited by a team of professional HVAC technicians.  This is absolutely advised.  That said, though, there are certain things that your technicians should be doing to effectively inspect the rooftop unit.

General Power Check Just as the first step to figuring out why a television has suddenly stopped working would be to check that it is still properly plugged in, the first step in this investigation should be to ensure proper power supply to the system.  The technician should shut off- and then turn on power again to check that the system is being properly supplied and also to gauge how the unit control board responds to the temporary loss of power.  Temperature set points can be changed to check that it results in the proper response from the system.  While the power is off, all electrical connections should be checked and tightened, as necessary.  In some cases, replacements may be necessary.

Close Visual Inspection This is basic stuff, but it is important.  The tech should look for signs of damage to coils or to the condenser.  Ice buildup or excessively dirty coils can point to problems that should be addressed.  Air filters should be inspected.  Dirty coils should be cleaned, dirty filters should be replaced.  And, it may be necessary to recharge the refrigerant, if there is ice buildup.  If this is the case, it is also important to look for any signs of refrigerant leaks.

Double check factory installed temperature sensors This can be done with a simple handheld infrared sensor. These can be purchased from SRP controls. Also, the infrared sensor can be used to check temperatures across heating and cooling coils to ensure there are no internal issues.