Actual question: how does the layman check for working AC in the dead of winter?

"Dr. Zoidberg - RIP Oppo" (thetomselleck)
01/08/2016 at 15:17 • Filed to: Car buying

I might be looking at a vehicle tonight that allegedly has working AC (it’s an older car so to think it might not is perfectly reasonablein my mind). But I’ve never owned a car, ever, with working air conditioning, and generally know squat about cars. It’ll hit below 35 tonight, so I don’t really know how to tell if it were actually working or just blowing cold outside air. Any advice?

DISCUSSION (12)

Nibbles > Dr. Zoidberg - RIP Oppo
01/08/2016 at 15:22

Hit the button while idling and note any change in engine load. If change exists, compressor is working and A/C is likely good. If no change, system is under or uncharged, or there is an issue with the compressor. You can also make a visual check - have someone push the button and watch to see if the compressor clutch kicks in.

As for testing intensity, if the car’s front window is foggy you can hit the A/C and see how quickly it defogs.

Textured Soy Protein > Dr. Zoidberg - RIP Oppo
01/08/2016 at 15:24

First run the defroster with the ac off and on recirculate to get the windshield good and fogged up. Then switch over to outside air and see how long it takes to defrost. Repeat the process a second time but add the ac to the fresh air. If it defogs noticeably quicker this time, the ac works.

Wrong Wheel Drive (41%) > Dr. Zoidberg - RIP Oppo
01/08/2016 at 15:26

Cold AC air definitely feels different from just regular cold air from outside. It is the relative humidity of it I suppose which feels different. But that is still difficult to really tell from. I think you could alternatively run the compressor and just make sure it is cycling properly and not quickly turning on/off.

Smallbear wants a modern Syclone, local Maple Leafs spammer > Dr. Zoidberg - RIP Oppo
01/08/2016 at 15:26

From most to least practical. (I'm not sure 100% whether these will all work either)

Start car. Let it warm up. Watch the revs and see where they stabilize at. Turn on the A/C, and if you feel the engine load or see any blib/increase in revs, the compressor should be working at least.

Warm the car up just enough to be tolerable (so that you don’t misinterpret a temperature drop), put it on recirculate, and wait.

Let temp stabilize, turn on A/C, measure vent air temp with a thermometer?

Aquire device for measuring humidity. Do not attempt to warm car, keep cold air blowing but measure humidity. Turn on A/C, wait, then check again. Working A/C should (theoretically) dehumidify the car.

jariten1781 > Dr. Zoidberg - RIP Oppo
01/08/2016 at 15:45

Run heater on recirc from face vents until comfy or warm, drop temp to min (no a/c, still recirc) verify still blowing out interior ambient, hit a/c button verify change. Using a thermometer at the vents is best but the back of the hand works alright.

Bullitt Ride > Textured Soy Protein
01/08/2016 at 15:58

This. I was just going to say hang out in the car until it starts fogging up then turn the AC on. If fogging goes away then it’s working to some degree.

AMGtech - now with more recalls! > Dr. Zoidberg - RIP Oppo
01/08/2016 at 16:24

What kind of car?

If it has a cycling compressor clutch you can watch it kick on and off. Depending on engine size you may not notice a change in engine speed or load.

If it has a variable compressor (usually just newer or higher end cars), good luck.

Dr. Zoidberg - RIP Oppo > AMGtech - now with more recalls!
01/08/2016 at 16:55

It’s over 25 years old and lacking in cylinders. So yeah I should hopefully feel some loss of power when I kick it on. Thanks

Dr. Zoidberg - RIP Oppo > Dr. Zoidberg - RIP Oppo
01/08/2016 at 18:00

Thanks to everyone who replied!

Eric @ opposite-lock.com > Dr. Zoidberg - RIP Oppo
01/08/2016 at 20:44

Even on a V8 of that age, you’ll feel the compressor going on.

The only advice I have is to check for air humidity, if you can feel it. A/C will notably dry the air out. If you run just the fan then turn the A/C on, it’s usually fairly obvious that the air is drier. It’ll also make the winds defrost super fast vs. just the fan.

In my experience (could be wrong), a bad one usually smells weird and/or heats the car up when on (seriously, even in the winter).

Dr. Zoidberg - RIP Oppo > Eric @ opposite-lock.com
01/08/2016 at 20:45

Thanks!

pImpOfThePerverse > Dr. Zoidberg - RIP Oppo
01/09/2016 at 04:32

I think most types of broken ac (no pressure in system, broken compressor) will blow hot even in cold weather.