Why only one fan working with A/C on

PRNCENGREASCOVRALL

MEMBER
2004 SUZUKI AERIO
4 CYL
2WD
AUTOMATIC
200,000 MILES

Well for starters, I believe I have a thermostat issue due to the lower hose being cooler than the top hose after 5min of operation, but other than that, my question is shouldn't both fans be running if the a/c is turned on? I only have one currently operating if I turn on the a/c. Another question would be, if the thermostat needs changing is the ecm being told it's hot by the temperature gauge so that it may signal the first fan to start operating, or is the fan issue a totally seperate problem in itself? Or will changing the thermostat eleviate that problem? A WHOLE TOTALLY SEPERATE ISSUE, is once I noticed my Aerio getting warm, I noticed that when I rev up the engine in park, the car seems to surge forward just a bit, as if it is wanting to go for a drive. What would be the cause of this issue? I don't drive this car regularly, as it is my wife's daily driver and I am just the lucky one told about the issues when they are seemingly a real issue. Please any help or knowledge you may be able to offer me would be greatly welcomed so that I may get my wife's car repaired and her happy and moving again. Thank you in advance for your time and help.

1 Reply

STEVE W.

MECHANIC
13,029 POSTS

Actually all of what you describe sounds normal. The lower radiator hose will be cooler as the coolant doesn't start to circulate until after the thermostat opens. However there is a small hole in the thermostat that is designed to prevent air from being trapped behind it. That will allow a small amount of heated coolant through and warm up the coolant on the other side. Being an 04 if the thermostat was open it would set a code P0128 and the engine would take a long time to warm up. The AC only operates a single fan to keep the evaporator from heating up. The second fan is controlled by engine temperature and if it does get to warm it can also turn on both fans at high speed. The surge forward in park is likely fluid drag inside the transmission coupled with engine torque.