never understood this. lets say youre in the car, ac on and on coldest setting. Now, its too cold so you turn the temp know a tad to the "warmer" direction, many knobs have a red line and blue section line. What happens when you turn up toward that redder direction to "warm" up the cold ac?? Does the comp compress less, as in compressing less frequent? Or does the system "mix" the same cold air with some heater "hotter" air?
beware of the arrival
Could be both ways depending upon the system. Most late model systems use the reheat system and move a blend door. Early systems used an adjustable thermostatic switch.
Still have a vehicle with an dash adjustable heater control valve, very slow responding. Heater core is always after the evaporator and completely dependent on it. Blend doors where the heater core is always red hot are far easier to adjust. Normally don't fool with adding a valve to the heater core as that heater core is now part of the cooling system. To do so can burn up an engine.
Us old timers would rather freeze than add heat to an AC system, AC system is completely independent of the heater system. And feels worthless to us to heat cold air. Good old POA systems and with the newer variable displacement compressors are far superior to that fix orifice system where the compressor is constantly switched on and off, either working full blast or not at all. The variable displacement compressors run all the time, but the load they put on the engine is proportional to the ambient temperature. Sure saves life of the compressor when expected to accelerate from zero to engine speed in a split second.
With automatic climate control, lose complete control of your system, a silly-con diode does that for you constantly varying the blend door to reach that preset temperature. Even changing the position of the mode doors.
In practically all systems, if the temperature is a tad above freezing, switching to defrost switches on the compressor. In my experience, next to worthless, particularly in a CCOT system where the compressor is constantly cycling at a high rate. With cold seals and stiff oil, that is when wear really occurs and leaks start. Your own breathe is the major culprit for steaming up the windshield, when driving alone until the car warms up, just crack open the window that clears the windshield instantly. Can't do that with the wife aboard, but on some vehicles, added my own switch to kill the compressor. Getting too old for that now, LOL.
One rule I have followed for years, is to switch off the compressor about five minutes before getting home with the blower at max to fully dry out the evaporator. Certainly saves on fungus buildup and even corroding the evaporator. Plus my cars don't pee all over my garage floor.
Geez, thats good info, Nick. Thanks, Man. And thanks to douglas too. I suspected a smelly fish here. I hate spending gas to cool ac then to warm it up a bit with hot heater core air!! Good to know.
Oh, Nick, is that "variable displacement" same as , for example, a V5 compressor some GM cars had? Does the "V" stand for variable? My sunbird has one, and yes, it runs constantly, I think.
beware of the arrival
Mythbuster's had a segment on this, but really can't be conclusive with only two vehicles. But their conclusion was, driving below 45 mph, better fuel economy with the AC off and the windows down. Above, better to roll up the windows and turn the AC on for better fuel economy. V-5 or 7 is variable displacement based on the same principle as the old POA system where the compressor always ran.
Except where the POA would bypass the refrigerant to reduce refrigerant flow through the compressor, the displacement is decreased. TXV systems add the variable valve in series, but still keep the compressor head pressure high, just tend to reduce the cycling of the CCOT system a tad.
In regards to adding heat to your AC, far better option than to face the consequences if the wife is riding with you.
I've never understood why so many Climate control systems KEEP the A/C ON even at 32 Degrees Setting, e.g on hot setting, it keeps the compressor turned on, and no Defrost is not selected either,
I've had 3 different cars that do this. Is there any specific reason?
First off it's simpler to build it that way. Also, allowing the evaporator to run warm results in high humidity from the vents. Air comfort is a lot about humidity not just temperature.
Air can hold as much as 32 g/m3, that is 32 grams per cubic meter at 30*C, at 0*C this drops down to 4 grams per cubic meter, both at a relative humidity at 100%, at 50%, far more common, drops down to 2 grams per cubic meter. So really not that much humidity to begin with. When 2 grams per cubic meter is heated, by the heater core to 25*C, that relative humidity drops down to about 10% RH. So what is this about excessive humidity.
What does happen in running the compressor at these much colder temperatures, it develops leaks quicker, and with the thicker refrigerant oil, uses more gas to spin it, and also wears out quicker.
Wouldn't use the word simpler to build it that way, cheaper is a far more accurate word. When fuel economy became an issue, some ACC systems did add an Econ button, but practically all vehicles switch on the compressor even today in the defrost mode. From my experience, doesn't make a damn worth of difference.
Easiest way to work around it, is to cut a rectangular hole in the left lower dash panel, mount a rocker switch, and break into the line that feeds the compressor coil. Been doing this for years so my compressor would last much longer. Would be different if you lived down south.
88 Supra is the same way, with the AC switch off, the compressor is off. With domestic cars with that AC switch, may only find a couple of mode positions where that AC off switch really works. Our old 98 Ford ZX2 was that way, as I recall, Vent and Heat was about the only positions where the compressor was off regardless of that AC switch position.
It also took some time to train my wife to switch off the AC before parking the car overnight. Her previous history was if not bad odors, her evaporator was constantly rotting out coming from a warm climate. Stepdaughter was a compulsive mode switch rotator. Her compressor didn't last very long in her ZX2, plus the odors.
They don't even mention this in any owners operator manual that I have read.
They do panic if a small stone gets stuck between the brake rotor and that shield. And what is that odor?
It's got to blend A/C air with "heater" air. When you move the temp control lever, it moves the valve to either let water into the heater core or shut off the water to the heater core. So when you are too cold and move that temperature lever, you are in fact sending a bit of water through the heater.
Motorhome has a heater valve that brought back memories of when all vehicles were that way. Takes a long time to respond and certainly a tendency to over control. So much happier with a blend door, response is almost instantaneous.
But this is only in terms of operation, so much easier to replace a heater valve than say a 98 Ford blend door. Have to recover the refrigerant, remove the entire evaporator box, take that apart, just to get at that blend door.
We've updated our forums!
Click here to visit the new forum
Copyright © 2016 Arizona Mobile Air Inc.