Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Air conditioning is always on

I have a 2004 Nissan Sentra, manual transmission.

The air conditioner seems to always be running in this car. There is a button that is pressed to turn the air conditioning on/off. However, no matter what position this button is in, the air conditioning is running.

Any ideas of what could be causing this or how I can fix it?

Thank you in advance, Ron

Have you watched the AC compressor to verify that the AC is on?

On many vehicles the AC compressor will run if you have the HVAC controls set to “defrost” or “floor and defrost.” Could this be the reason the AC is always on?

No, I have not checked that, but I will. The second part of your reply where you mentioned when HVAC controls are set to ‘defrost’ or ‘floor and defrost’. I have not noticed if that is when the problem is happening. That might just be what’s going on. Because what I’m really seeing a lack of power in the car when this is happening, just like what happens when the AC is on. I’ll check and determine if this only happens during those settings and what happens when it is set to other things like ‘floor only’.

If this is the case, is there any way to prevent this from happening? It seems to suck power from the car when I’m trying to accelerate?

Thanks again. Ron

Yes, the AC will take a few HP from the engine. A few. It shouldn’t make a major difference in acceleration, especially with a manual transmission. Perhaps there is another problem.

If you floor the throttle the AC compressor should disengage, regardless of the HVAC settings. The trouble is, this only works when you floor it, so even if you push the gas pedal 90%, the compressor will still be running, and adding its load to the engine.

Set the heater control that directs the air flow to “floor” or “floor and upper vents”. These should be easy to differentiate from the “defrost” and “floor / defrost” settings. Consult your owner’s manual if you still have it.

Unless it is very moist air in your area you should not need the “defrost” and “floor/defrost” to keep your windows clear and the car at a comfortable temperature. When you do have fogging of the inside of the windshield by all means go to the defrost settings until the windshield is clear. Check the “fresh” and “recirculation” air settings too. These are buttons that normally should be on fresh air in most situations.

The AC should not be running all the time to keep you comfortable until the temperature where you live gets in the high '70’s and '80’s.

The a/c compressor is supposed to run on defrost. I guess you could prevent it if you pull the wires of the compressor or pull the fuse. However you might need it this July.

Of course turning it off is generally not a good idea unless you really like trying to see out a foggy window.

My car is a bit weak/AC at low RPM due to a small engine like yours. If you nearly floor it the AC disengages temporarily and you get the power as if AC was off.

A few HP significant at low RPM is a lot since most small engines produce very little HP in this range.