I have a couple questions about AC

[dcu1976]

I have a 97 MGM, Since I live in Florida I use the AC all the time. One question I have is what is the difference between normal, and MAX AC? Does it just make the blower run at max speed(unless you change fan speed), and/or does the compressor stay running, compared to normal where it runs intermittenly? I know nothing about AC, so please forgive my ignorance but I noticed some few things that I think is very interesting. 1st when running the AC at normal, it does blow nice and cold but the engine temp runs hotter. On the gauge, the needle points to the top of the thermometer pic(but still in safe range). Now when I run the AC on MAX the engine temp is right where it always is(midway on gauge), So why would runnng the AC on normal cause the engine to slightly hotter compared to max where the engine temp is where it should be? when sitting in heavy traffic/red lights, I usualy swtch to Max AC to let the engine cool down, confusing to me because it seems to me the opposite would happen. I hope I haven't confused anyone. Thanks!

[1987cp]

I seem to remember being told that the MAX is the recirculating mode (re-cools already cooled air from the cabin), but that's backwards with respect to a dealer mechanic once telling me to put it on MAX for a few minutes before switching it to normal A/C mode - if the car is really hot inside, you'd think you'd want to start by drawing in slightly-cooler outside air until the cabin is cooler than it is outside.

[johnunit]

MAX AC does indeed indicate recirculating (taking air from the inside of the cabin, instead of the fresh air vents). It will generally cool the car off faster because by the second time through the air is cooler than the ambient temperature most of the time.


I'm not sure why you're having overheating issues. unless this is a climate control (set a target temperature instead of just asking for hot or cold air) there should be no difference in load on the engine between the two settings.

[gadget73]

Running the AC on normal actually works the system harder since its cooling outside air. Lets say its 100 degrees outside, and the air coming out of your vents is 40. You're dumping 60 degrees with the AC system in normal mode. Lets say the inside of the car is 80 degrees, and in max mode you're still getting 40 out of the vents. Now you're only dumping 40 degrees in the AC system. That heat has to go somewhere, and thats the condensor that lives in front of the radiator. Hotter air in = more heat at the condensor = hotter air passing through the radiator = hotter engine. Its to be expected. As long as the engine temperature gauge stays in the normal range, you're OK.

[dcu1976]

Thanks for the replys!

Running the AC on normal actually works the system harder since its cooling outside air. Lets say its 100 degrees outside, and the air coming out of your vents is 40. You're dumping 60 degrees with the AC system in normal mode. Lets say the inside of the car is 80 degrees, and in max mode you're still getting 40 out of the vents. Now you're only dumping 40 degrees in the AC system. That heat has to go somewhere, and thats the condensor that lives in front of the radiator. Hotter air in = more heat at the condensor = hotter air passing through the radiator = hotter engine. Its to be expected. As long as the engine temperature gauge stays in the normal range, you're OK.

What you posted makes perfect cents, I guess thats why my engine runs warmer on normal AC then when on MAX. The engine temp is always n the safe area, just a tad higher when running normal AC.

Thanks everyone who posted replys!

[1987cp]

So the logical procedure really is the reverse of what the service techie told me - i.e. run on "normal" A/C to help pump hot air out of the car, then switch to "MAX" to keep the cool air cool.

Glad I was forced to think about that for a bit, since I've been slightly unsure about what to do ever since I got my A/C working again last summer.

[gadget73]

you can start it on max and leave it there. Doesn't much matter. It is somewhat louder on max since its sucking air from inside vs outside but unless you have the fan on full blast, that probably won't matter much. I know my truck used to start smelling funky if I left it on max for too long. Don't know why, but it got a sort of wet dog odor to it that switching to regular ac took away. I think at some point I sprayed some of that AC deodorizer stuff through the evaporator and it went away. Having it on normal mode does have the advantage of forcing some fresh air into the vehicle, particularly useful if you are travelling with people who eat lots of gassy foods or whatever.