I’m the OP, and I did read every page of the manual first day I got the car. RTFM, right? Not sure how it helps.
To repeat: most times that I need demisting, a gentle current of warmish air is plenty, no AC needed. But that’s not an option with this car. The bigger issue is de-icing on the outside. I want max heat, not AC. And despite what some have said, mine comes on even at 10 degrees F. Perhaps it’s another defect, but it does.
Wouldn’t be such an issue except that all the washer fluid I’ve had in the last few years ices up instantly in cold weather. That really is a safety hazard! Anybody know if adding a little methanol, denatured alcohol or radiator antifreeze to the tank would be OK for pumps, seals, etc.?
You can disconnect the wire to the AC compressor clutch to disable.
It’s a single thin wire that goes near the compressor pulley with an easy to pull off connector.
In the spring put it back on.
Not really Ellis, the compressor uses the same controls when using A/C or defrost. The indicator on the dash may show that the A/C is enabled but the evaporator temp sensor will switch the clutch off below 32 degrees F., unless you want an ice maker? There is also a low pressure cut-out switch or an A/C pressure transducer. Normally there must be more than 25 PSI before the compressor will turn on. At 10 degrees F. R134A has 12 PSI.
Nevada and others - it’s not just the light. I can easily feel the car slow down slightly when switching on the AC or setting air flow to defrost position. And I can easily feel the air being cooled as well. Perhaps the temp sensor is inside the dash or near the engine? It certainly seems to put the AC on when it’s cold out.
This is a convenience feature. Your windshield will clear a LOT faster with the A/C on and you don’t need to use nearly as high a temperature setting to clear it when the A/C runs. In weather near freezing and below, the compressor will not run, even if the A/C lamp is indicated. Either the pressure in the system is too low at that point to allow it to start, or a temperature sensor makes the decision.
“Elihu, You are right, the A/C comes on with the defroster no matter how cold it is”
That’s not necessarily true.
From pages 83 and 84 of the 1996 F-150 manual
“Select DEF to obtain maximum air flow to
the windshield. Rotate the center knob into the
RED area for the air temperature required to
defrost. When the outside air temperature is
84
about 50°F (9°C) or warmer, the air will be
dehumidified to remove moisture. The air can be
cooled or heated. Rotate the knob on the left
to increase the air flow”
In this case, only when it’s over 50F or thereabouts, will the A/C compressor run when the defrost setting is selected.
FoDaddy Your post doesn’t say that the compressor goes off. I still contend that the compressor will come on and stay on no matter how cold it is. (at least it does on MOST cars). I haven’t owned many foriiegn cars.
I’m not sure I buy the “cars aren’t as drafty nowadays, so they need a/c” argument.
If you have outside air (no recirc) selected, then for every CFM coming in through the vents, there’s (by definition) a CFM going out, somewhere. If this weren’t the case, cabin pressure would climb until CFM(in)=CFM(out)…or the car blew up from cabin overpressure (whichever came first). I mean, cars might be less drafty, but they’re not Boeings!
Granted, selecting recirc for long periods of time is a good way to steam the windows…but that falls under “operator error,” not an intrinsic reason to require a/c use with defrost setting.
When I have my druthers, I use a/c for “de-fogging” (getting rid of fog already on the windshield), and a/c off for less-demanding “anti-fogging” (keeping an already clear windshield from fogging up).
I think my previous post was not exactly clear when I said the AC does not work below 40°F or something to that effect. I did not mean that the compressor does not come on.
In the evaporator, there is an orifice known as an expansion valve. Below 40°F, that orifice closes down and stops the flow of freon, so for all practical purposes, the AC is not working. The build up of pressure on the high side and drop on the low should shut down the compressor, but you will feel it when it initially kicks on.
Even if the compressor does not kick off, with that much pressure on the high side and drop on the low side, there should not be much drag on the compressor because it is not compressing anything.
@keith: If the TXV closed and “stopped the flow of Freon”, a line would burst or something would be damaged if the compressor was still running. Plus some systems do not use a TXV.
The manual on my current car states that below about 35F, the A/C will not run. I have observed this behavior on this car and my last several.
" If the TXV closed and "stopped the flow of Freon", a line would burst or something would be damaged if the compressor was still running. Plus some systems do not use a TXV"
Not necessarily. The maximum pressure is a function of static line pressure times the compression ratio of the compressor. It can’t go higher than that.
I have an '03 Honda Civic, which should have the same controls and AC set up a the OP’s '02, The airflow control knob has a setting for full defrost, and a setting for defrost and floor. When you move the control to either of these settings on my '03 the AC compressor engages, but the light on the AC button does NOT illuminate. So, the AC compressor is “ON” but the dash light which is integrated into the AC button does not go on.
I’d rather be able to turn the AC compressor off too, but it doesn’t work that way on this era Civic.
Elly, my description is of the older AC systems. Many of the ones today are completely controlled by the vehicles computer. On our 97 Honda, there are 10 inputs that the computer uses to determine whether or not to send voltage to the compressor clutch. I’m sure there are more than one way to control the AC system in modern cars.
Well, the temp here this morning is 25 degrees, if it weren’t for about 3 inches of snow on everything, I would go out and turn on my defrosters, raise the hood and see if or how long the A/C compressor would run, but I will do it some other time. I bet it runs as long as I have the defroster on. BTW my car is an '09.
What you need for cold weather is “winter mix” windshield waser fluid.
I’d avoid methanol and definitely coolant antiifreexe, which is designed to leave a film (remember it also leaves corrosion inhibitors and lubricates your water pump).