Well the next time the tempearture is down around zero F, turn on the A/C - if the compressor enagages you'll know it becasue of the squealing belt sound (if you are lucky) or the grinding sound of a compressor disentegrating (if you are unlucky). It only takes around 6 psia to turn R134 liquid at 0 degrees. Compressors aren't really designed to pump liquid - at least not for long. At 70 degrees F the pressure in the system should be over 50 psi with the compressor off.
Take a look at
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- The pressure switch inhibits the operation of the compressor when the refrigerant low side pressure is below 28 psi, or above 455 psi. At 32 degrees F the presuure in the system is going to be below 28 psi, so the compressor shouild not run at least when the vehicle is cold. Once the vehicle warms up, the underhood temperature may warm things up to allow the switch to close and the compressor to run, but if you are driving along in cold weather, the flow through the AC condensor should keep the refrigerant cold which will prevent the compressor from engaging. The A/C system also has a thermistor that provides temeparture information to the A/C controller (see
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) I suspect this actually inhiits compressor operation based on the indicated temeparature at a temperature higher than the low pressure switch does, but the Toyota manual does not provide details on the actual operation of the control circuit in resposne to the thermistor input. See
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The thermistor resistance is only shown over the range from 32 F to 77 F. I think they use it to switch off the compressor at low temperatures. But for sure the low pressure swwitch will prevent engagement of the compressor at tempertures below 32 F (assuming a properly charged system). Ed
If the truck is adjusting itself properly, there will be no effect on the tach when the compressor is engaged, or not. Or the effect will be so small as to be unnoticable by looking at the tach.
But whatever. Your entire argument is beside the point of the topic.
On Jul 28, 2:05=A0pm, "C. E. White" wrote: All modern
That's how most of them work I think. Low pressure switch.. Pretty sure that is how the one on my 05 works.. Also, I'd have to double check as I really don't use defrost very much, but I don't think my compressor light comes on in defrost mode, unless the compressor button is already pushed in. If it's winter and I turn on the defrost, I don't think my light comes on even though the compressor will be running. But I'd have to double check that.. Like I say, I hardly ever use defrost.. But I know for sure mine uses a pressure switch as it will often cycle when the car is cold inside and the engine is idling. With the lower idle speeds the pressures drop and bingo, off it goes.. You can see the rpm's change when it drops in and out. With the A/C idle up solenoid, mine actually idles faster with the A/C on, than it does with it off. Once mine is cooled down, my register air will be 40-45 degrees. Often right at 40 with the car fully cooled down. I keep a "pen" thermometer stuck in the drivers side vent.. So won't take much of a pressure drop to click it off. Just stopping at a light will do it after a few minutes. I'm fairly certain the same system is what cuts it off and on in the winter. And I agree.. Running the compressor a few times in the winter is actually good for the seals, rather than causing extra wear. It's seals that take a set from sitting too long that usually cause compressor seal leaks. Even if a car didn't run the compressor in the winter as say in old cars, I'd still run it myself every once in a while.
I wish you lived close to me so I could bet you $5 the compressor doesn't run (at least till the car is warmed up) on a day where the temperature is below freezing.
Well that's nice to know, at least. I thought maybe the heat would be fighting the AC when it was 0 degrees outside.
I'm not sure. When the temp gets too cold outside, home and car heaters just arent designed for it.Just like it's hard for AC to keep up when the temp hits 110, it's hard for heating to keep up when it hits 0. They just dont design the systems for those extremes.
I wonder if this way of thinking comes from the socialist "cradle to grave" mentality, where they think that people are too stupid or incompetent to make their own decisions, so everything has to be decided for them?
But next time you're out on a cool and damp day, take a look at the cars you're sharing the road with. An amazing number of them will have fogged up windows, because people don't get it--even when they can't see outside the car.
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