Cooling Fan Question

I have a 2002 Grand Am GT with the 3.4. I let my car get up to full operating temperature and the cooling fan doesn't seem to come on. I thought maybe something was wrong with it but when I turned on the A/C, both fans kicked on. I always thought one fan worked whenever the car was at operating temp and both kicked on when you're running the a/c. The car blew the coolant resevoir at the seems(again) so I replaced it and also changed the thermostat then bled the system. I'm hoping it's not a head gasket. If anyone can give me some insight on the cooling fans I would greatly appreciate it. Thanks

Normal!

The thermostat open at like 85C (I don't have the exact temperature)
Low speed at 106C
High speed at 110C

The AC turn on the fan at:
low speed 190PSI
high speed 240psi

High speed is also selected on some DTC code

Low speed work by putting both fan in series, effectivelly sending ~6V on each fan
High speed is both in parallel, so each get 12V

Try this: with the engine cold, squeeze the radiator hose coming off the thermostat. It should be easy to squeeze. Then start the engine, and squeeze the hose again. If it gets hard/builds pressure quickly (few minutes or less) then u may have a blown head gasket leaking engine gases into the cooling system. After 10-20 minutes, system should come up to normal temperature (~200F) and cooling system pressure (7-10 psi), which you should be able to feel by squeezing the hose again. If it never comes up to pressure, you've got a leak somewhere in the cooling system and your system will boil over. Coolant must be under pressure to keep from boiling at normal operating temp.

1st place to check for leak is reservoir cap; did your new reservoir come with a new cap?

Hope this helps.

I had a similar problem with my Venture van. I changed the coolant temperature sensor and that fixed it. At first, I did not think that was the problem because my temperature gauge on the instrument panel still worked fine.

disconnect ect sensor and fan will come on that is the best test. pcm will see -38 F which means open in ect sensor circuit and as a preventive measure will initiate fans.

thanks, i'll try that. I did replace the coolant temp sensor last year with a acdelco but you never know..