On my '02, I'm not sure which settings have the A/C on. Some are obvious ( the two with the snowlfake, duh).

I think it runs also with the defrost on, true?

If it runs with the defrost on, does it turn off below a certain temp? I mean, there's not a lot of moisture to remove from the air at 15°F!

Does the A/C operate in more positions that A/C and defrost? What about dash vents? Floor? Bilevel?

I thought the A/C ran in bilevel as well, but only if the temp is set low enough to require cooling below ambient....

Is there anywhere I can get a comprehensive explanation of my HVAC setup??

IIRC, the owner's manual was worthless...

Justin

 

From what I have read the A/C is only on at 3 settings: A/C, Max and Defrost. There is a BOMB on TDR to add a switch so you can turn it on and off at any setting.

 

The A/C will run on any "A/C" setting, as well as defrost or bi-level. Most modern cars do this. There are two obvious reasons; probably several more I don't know about. The two I do understand are: 1. The defrost is much more effective in any weather with the A/C on, drier air defogs better. 2. This way, the A/C is cycled frequently during the "off-season" months, so leaks are less likely to develop in the system. As I say, there are more reasons I don't know about, but I guess I just woldn't worry about it being on.

 

I don't worry, so much.

It's more that I think it's wasteful and inefficient. The A/C doesn't need to run in weather below 40° for anything I can think of.

True, drier air defogs better, but when it's really cold, the air is already incredibly dry.... Thus, the A/C is a waste.

It IS good that it gets cycled, though. A/C always seems to be more reliable in the South, and I suspect that's because it's almost always being used.

Justin

 

The A/C cycles in 5 settings. Both A/C spots, bi-level, heater/defrost, and defrost alone. Its almost impossible to defrost while its wet out without the A/C compressor on. It pulls the moisture out of the air. Helps dry you too in wet weather. Its also a good idea to cycle the A/C compressor throughout the year to stop freon (spelling?) leaks. It can leak out the seals when not used for a long time and is VERY expensive to replace. Plus I'm sure not to many shops will replace anything without checking the system for other leaks, which means more money.

 

Freon is pretty cheap actually (especially R134a), the leak wouldn't be though. A couple years ago I was using the A/C in my Talon almost everyday, sometime that winter apparently a seal blew and it hasn't had any A/C since. I'm EPA609 certified to buy R12 but I doubt I'll bother as I probably won't use the A/C in it anymore now anyways as it is just a backup/ toy car.

 

When the temp is below 40* and you have wet boots or a wet coat, the A/C is very usefull. I know this first hand from plowing. You get in and out of the truck a bunch if you use a salt spreader and the moisture you let in used to fog up the ramcharger something fierce. A/C (defrost) was fixed and it was night and day clearing the fog out. It took about 15 minutes of hot heat out the defrost to clear the windows without a/c, and then it was so hot in the truck you had to plow with the window open or bake. jmo

 

I disabled the A/C on my trucks the first winter I had them, no fun with cold air blowing in at minus 15. I now have the choice of A/C or not in every vent position, 15 minute job on 12 valves with no parts, a little longer on 24s with an additional switch required.
Instuctions here> http://dodgeram.org/tech/repair/HVAC/Defrost_AC.htm

 

one thing about defrosting, when you heat the air the humidity goes up. What that means is that at 15 deg. you may have a relitive humidity of 2 but as you heat it up to defrost your windows it will go up as the temp rises. Thats the reason you need the AC on in defrost, it is acting as a dehumidifier, not an air conditioner. It takes alot more to defrost your windows with just the heat . It is also true that the best air conditioning systems are the ones that run the most, the worst thing you can do for your ac is to not run it.

Chris

 

Guess you have not been in the east in the winter.

 

ChrisM55 is right except for the RH comment.

RH decreases as temperature increases. That is why dew point (the point at which water condenses from air) is always at or below ambient air temp. Heating the defrost air increases the energy in the airstream avialable to turn the frost to vapor, and having the a/c run as it does on the defrost setting will dehumidify the air, lower the vapor pressure in the air and further increase the rate of evaporation.

dw

 

I just got back to ontario from a trip to BC. While I was there, the snow storm hit Fort St. John, and the weather was cool and rainy the rest of the trip. I always leave the defrost running in my truck, so the ac is always cylcling.

At the end of one day we pulled into a camp ground, i set up the camper and got back into the truck with my wife and child, and tried to warm my hands. The control doors had frozen up, and it would not switch from defrost to vent.

I looked at the plastic hvac piece that holds the condenser and it had frost on it.

In the morning the frost was gone and the controls worked fine.

I am thinking of putting the BOMB listed in this post to prevent that from happening again.