My A/C has been conking out every now and then. How do I know it's something wrong with the compressor and not just need a recharge of R-134A?

 

Define: "conking out every now and then."

 

The air conditioning system has both high pressure and low pressure switches. Either one can cause the system to stop working, but not intermittently unless there is a wiring issue. Therefore, if the system works periodically, it isn't an issue with the R134A charge. It could be the pressure switches, the electricals/electronics in the heating and fan controls, etc.

 

I thought I noticed the A/C not working sometimes this past summer, but I didn't know if it was my imagination. Now it hasn't worked for 2 consecutive days...frustrating when your windows are fogged up.

I recently had a shop disassemble and remove the Honda aftermarket additional security system, which I think was wired up near the HVAC area. Coincidentally, my rear defroster icon quit lighting up about a month ago, after the shop removed the security system.

Maybe they're connected?

 

Let me understand. This morning when I woke up it was 0 degrees F. The East coast is having major snow storms (did you see the Phidelphia game Sunday?) and your profile say you are in New York state. Buffalo on one side and NYC other the other side of your state shows weather with highs is the 20's.

If you are trying to run the AC in this weather, it will not work. You are below the freezing cut off temperature for the evaporator. I can not begin to give you R-134 pressures with that low intake air temperature.

Try putting the temperature on hot , not cold when defogging the inside of your windows.

If you still have problems, post back here when the Outside Air Temperature (OAT) is above 70 F.

 

Whatever design it uses works below freezing (surprised me too). I don't know about below 0F. But yeah, I'd be more concerned at higher temps. I don't think they can even diagnose it if it's less than about 60F.

My last Honda the compressor would not engage below about 40F.

 

Common sense. Who said I had the thermo set at its coldest? If you have it set with any heat with the A/C on, you will (should) sense that the air is colder than it would be without the A/C on. Plus, I mentioned about the windows fogged up. Air conditioned air quickly eliminates the fogged up windshield.

 

true, what n9cv is saying is there is an outside temperature below which the A/C won't work. It seems like the temp sensor in the evaporator would prevent it from working below freezing ambient temps, but I know from experience it continues to work (others have commented on it too). I know this was around 40F on older Hondas but this isn't the case on GEs (I use the dehumidifying ability of the A/C with heat on mine too, on colder GA days). There may still be an outside ambient temperature below which the A/C compressor will not come on. The owner's manual doesn't specify and I don't think the shop manual does either, but I don't have access here.

It is a mystery. If in the past it has functioned for you at sub-freezing ambient temps and now it isn't, I don't know how to troubleshoot it, or if Honda would consider it a problem. If it performs ok when it's warm outside, I would suspect something with a pressure switch or temperature sensor that is performing differently at cold ambient temps than it did before.

Do you use recirculate a lot? Bringing in cold fresh-air will help with the humidity problem too.

 

Let's talk simple physics (or chemistry). If you bring in any air below 32 degrees and expect the AC evaporator to remove the moisture from it, that moisture would immediately condense on the evaporator and freeze there. There already is very litttle moisture in air below freezing so that really is not happening.

Take a look at the 3rd graph on this page:

Temperature and Moisture Holding Capacity of Air

As they stated, incoming air at 30 degrees only has 1/10 of the moisture carrying capability of air at 100 degrees. So take your cold air in, warm it up, with the heater core and blow it across the windows to de-fog them in defroster mode. By doing this you will end up with warm dry air at 100+ degrees at less than 10% relative humidity.

Automotive AC can not help with defrosting at these winter temperatures in the winter. It doesn't work that way.

The amount of refrigerant charge in your AC system determines how cold the system can get. In a motor vehicle we normally charge the system so it it goes to about 45 degrees. I have mine set for 40 degrees in the summer as measured at the air vent. Anything colder and it freezes up.

Now in the summer the whole game changes and AC pre-cooling the incoming warm moisture laden air extracts a lot of moisture from it. Running the AC definitely will help in warm / hot temperatures.

 

I would beg to differ. In the absolute coldest days of winter in Montreal Canada (-20F) fogging of the front windshield is at its worst. The car is hot on the inside with the passengers sweat or any moisture inside evaporating and the windshield is cold on the outside causing instant fog. The only possible way to drive is with the front defogger on which activates the compressor. This eliminates the condensation nearly instantly and turning this off causes the condensation to return in a matter of minutes.

So just for the record, I've used the A/C in extreme cold and it does work. It actually works very well.

 

You're right on all points.

Now go out and run the Fit's A/C when it's below freezing outside and tell us it:
a) doesn't run the compressor
b) if the compressor runs it doesn't help dehumidify the air.

I wasn't a believer till actually trying it. I can't explain it, but there it is.

Yes:
This is running on fresh air
the ambient temperature is below 32F

And I understand A/C theory and am pretty familiar with the Fit's design. At first I thought this might be due to the evap coil being after the heater core, but no, air passes through the evap coil first.

it is a mystery.

go on... try it. you know you will

 

I tried to explain it. Maybe someone else can do a better job.

Just because the AC mode is selected and the indicator is on, that does not mean that the compressor is running and the evaporator is cooling. Without the evaporator cooling to a temperature lower than the incoming air, you will extract no moisture. If you want to, you can set this up and look to see if the compressor is running at -20 F or -20 C.

Most modern vehicles turn on the AC mode when defrost is selected, but when the incoming air temperature drops below 40 to 45 F, the compressor is not running and the evaporator is doing nothing.

 

This part isn't correct. In most cars (and especially in the FIT), you can feel the difference in power when the compressor kicks on as it zaps power from the engine. Even in the coldest temperatures (Below Zero), I can tell when the defroster is on, just by the amount of power I don't have. The minute I turn the dial so the defroster isn't selected, It's like I've hit a turbo boost button and the power returns. This means the compressor is indeed running, even if not being (as) effective. The Ambient temperature in the car should be enough to keep the condenser from completely freezing over, especially once the car has warmed up a little bit. The added benefit of there being much less moisture in the air should mean that the system doesn't have to work anywhere near as hard to remove moisture as it does in the summer.


OP, I'm inclined to agree with others saying it likely isn't the compressor or the charge in the system. possibly one of the other components mentioned. Do you run into the same issue with the heat set to it's highest?

~SB

 

Let's try this another way. I have an Air Psychrometrics chart in front of me.

Let's take outside input air at -13 degrees F (-25C) It shows that air at that temperature can hold a maximum (100% relative humidity) of .64 grams of moisture per square meter. Now let's heat that air up to room / cabin temperature of 68 degrees F (+20C) The chart shows that the air can now contain a maximum (100%) of 17.3 grams of moisture. Raise that one more notch to 104 degrees F (40C) (a reasonable number for defroster output) and the 100% moisture content raises to 51. grams


Air temp 100% grams
-13 (-25C) 0.64
+68 (+20C) 17.3
+104 (+40) 51.0

So if you took -13 F 100% air and heated it to 104 F it would contain 1.25% relative humidity.

If you took the same air and only heated it to the same as the inside temperature of the car (68 degrees F) it would be at 3.7% relative humidity.

Both of these are pretty dry and uncomfortably dry for humans. I do not know how much more you think you could extract with your AC evaporator.

The Sahara desert usually runs around 25%. Occasionally it is lower is specific areas.
The Gobi desert average is around 31%.

MY point is even if running an automotive AC worked, the relative humidity of the input air when heated to defroster temperatures is so low that there is no moisture left in the input air to extract.

Do not run defroster on recirculate in cold weather. The defrosting action relies on warm dry air absorbing the existing moisture in the cabin and on the windows. That warm air then needs to be forced outside of the car and is replaced by more new dry coming in through the defroster.

HTH

 

Yes, the A/C would not operate at any temp setting. Yet it did before and on every car I've owned. Yesterday, I tried the A/C and it did work, but then I have to turn the car off. Seems like it's still intermittent.

 

Maybe you're forgetting that our breath inside the cabin adds a lot of humidity quite quickly, and that it needs to be stabilized with a dehumidifier. Remember that a lot of cabin air is still being recirculated even though you have it on fresh.

My AC compressor also comes on when below freezing, there's no question about it. You can hear the compressor fan turn on, and even feel the clutch engage while driving.

 

...no. Not forgetting.

 

I wasn't clear. The comment was directed at n9cv

 

This morning it was 11 Degrees F here in VT. Compressor kicked in when I turned the knob to defrost. How much benefit it does other than re-direct the air to the windshield may be another story. I wonder if what most people assume is the Air Conditioner removing moisture from the windshield is actually just the dry outside air being blown across the windshield. There are a few people on this board who have disconnected the A/C engagement switch from the defroster [so when you turn on the defroster, it is only changing the direction of the air, not kicking the A/C on]. They might have an idea of if there is a difference in speed of defogging the Windshield when the A/C is on or off.

Maybe both N9 and the rest of us are both partially right. Hmmmmm.

~SB

 

Seems like most if not all of you don't see the forest for the trees. Or maybe you rarely turn the A/C or the defog setting on, but when you do, the fog on the windows evaporates very VERY quickly. Almost immediately. If there is no A/C, the windows clear very slowly, if at all. So when your A/C stops working you know it. You can spew all sorts of technical formulas and data around, but empirically, the A/C works when on the defog setting or the A/C button depressed, and right now, my A/C is intermittently working.