Is this possible?? HVAC professionals opinion needed

[martin1234]

My parents have, what I believe are, "professional tenants" who are constantly complaining about the AC not working properly.  We had two different AC technicians check the system on two separate occasions and they said everything is fine - they both measured temperatures at the vents and in the rooms.  These tenants live on the main and first floor of the house. There are different tenants in the basement - the thermostat is in the basement and the temperature is kept on AUTO at all times.

One day the upstairs tenants complained that they had the temperature measured over 28C (82.4F) at 9AM when the outside temperature was 22C (71.6F) and over night the lowest temperature was 16C (60.8F).  The sun is being blocked by a house on the east side and big trees on the north side - so the sun doesn't shine through the windows or on the sides of the house in the morning.

*** Is this scenario possible assuming the AC was not working? ***

They would not allow my parents to come and check the temperature for themselves!

My parents lowered the temperature on the thermostat. And within 30 minutes the tenants upstairs claimed that the the temperature fell to below 26C (78.8F)

So from 28C (82.4F) down to 26C (78.8F) - a differnce 2C or 4F.  This house is 1900 square foot and I find it hard to believe that this is possible.

*** Does any HVAC professionl here think this temperature drop is possible within that time period? ***

Has anyone else have this sort of tenants?  I will get and install wireless temperature loggers in the future but I understand that they can be manipulated as well...  If you have a better suggestion I would love to hear about it too.

Thanks in advance for your input,
Martin