Heating, Ventilation plus A/C maintenance can be a extravagant thing to pay for, then i have no experience when it comes to diagnosing plus repairing an air conditioning unit or oil furnace.
If I had any problems with our Heating, Ventilation plus A/C device at our home, I would first have to turn to Google to find some answers plus hopefully succeed in self servicing plus repair, then the first thing I would try is to check the breaker because it could have tripped off.
I would be so embarrassed if I called a Heating, Ventilation plus A/C serviceman to come out for a maintenance plus the problem was only a breaker! The minute thing I would do is check the batteries in the temperature control! Something as easy as dead batteries could cause the unit to not work properly, then another thing to try to do is self-repair your air conditioning unit is to check your filter. If your filter is jammed up with dirt plus dust, it will affect the air flow plus possibly ice up the unit. Every so often, the unit itself just may need to be cleaned, then you could also climb up into the HVAC ducts if you’re comfortable doing so plus checking to see if you recognize air coming out of them. They could be dirty enough to be blocking air flow and, in this case, would need to be cleaned. These are some things to try yourself before calling in a professional maintenance corporation, however of course, sometimes dealing with cooling system maintenance can only be done by a serviceman.