I just had an experience that shows you why you probably should pay to get a licensed HVAC contractor to evaluate the systems during your due diligence of buying a home.
My buyers' inspector found the HVAC systems to be 11 years old but the systems seemed to be working the way they should. The inspector showed that there was a 16 degree difference between the input and output air temperature for the AC. The furnace was blowing hot air like it was supposed to.
But my buyers wanted to really have someone look over the systems so they got a HVAC contractor to come out and test them out for $89.
They found that one AC system was low on refrigerant and the other one was overcharged with refrigerant. The HVAC contractor had a refrigerant detector that detected the precense of refrigerant at both coils. They said that there was probably a small leak somewhere in the coils and it would need to eventually be fixed.
In our inspection amendment we requested that both AC units be replaced since repairing them with soon to be obsolete R-22 would not be feasible.
We had the company give us an estimate for $10,000.
The listing agent wanted to take care of it with the home warranty that they were providing but there are limitations to the coverage. Usually there is a maximum cap of around $2000/policy.
The seller agreed to reduce the sales price by $10,000.
So that $89 HVAC inspection saved my buyers $10,000
If my buyers had just gone by the inspector's report, they would not have gotten a $10,000 concession and would probably be having cooling problems next spring.