a/c and cooling tech

[POS carb]

OK A/C is kind of a mystery for a lot of people but it's actually very simple if you know what's in there and how it all works together.
Let's start with a parts list:
1. Gas (and a little esther oil)
2. compressor
3. condensor and evaporator
4. expansion valve/thermostat
5. fans and blower
6. reciever/dryer
7. high pressure and low pressure lines, relays, wiring, seals

That's it. The combination of the above parts reduces the temperature in your ride 50-70*... how?

let's start with the cooling. How do you reduce the temperature in a car's motor? You get water pump it through the motor and radiator, fans pull air over the radiator fins and cool the hot fins (which have become hot by drawing kinetic energy from the water) and in turn cool the water, which gets pumped back into the motor to draw heat off the head. Rinse. Repeat.

The A/C is very similar but it also utilizes 18th century physics, aka Charles' Law, V = kT (volume is proportional to temperature times a constant).

It all starts with the COMPRESSOR, it pumps the coolant gas (R12 or R134 nowadayz) into the CONDENSOR.
In the condensor the fans pull cooler outside air over the condensor fins (which are now hot from the gas inside) and condenses the gas into a dense charge and it continues on into the vehicle.
Once inside it goes through the expansion valve and thermostat. The EXPANSION VALVE lets the gas expand (duh) and flow into the evaporator. This usually comes with a thermostat too that cuts the gas flow if it gets too cold. Once inside the evaporator the gas is a lot colder and the evaporator's fins get cold too. The BLOWER pushes air from inside (REC) or ouside (FRESH) the vehicle over these fins and voila, cold air. The whole process is continuous and after the evaporator the gas is once again expanded and hot and gets sucked into the reciever/dryer low pressure side of the compressor.

Cooling problems
OK now that we have the basics down let's troubleshoot
Obviously it is a fairly basic in theory and operation and this makes it easy to diagnose problems

air doesn't turn on
1. does the blower motor blow air?
yes---> n/a
no-----> check fuses, diode, switch. If power is available at the motor's terminals replace faulty motor

System doesn't cool at all
1 check gas levels
ghetto---> push the pin in the LOW PRESSURE fitting, should sound like a tire when you're letting the air out if it has gas
real-----> get a pressure meter and hook up to the low side fitting, check that it is within the specified range (don't have my book here with me sorry)

*note if the system is not charged the a/c compressor will not engage until pressure is present.*

2. make sure a/c compressor's clutch is engaging, easiest way to tell is to use your ears...

[POS carb]

oops I hit post...
2) continued...
motor off-----> shut off all accessories and a/c switch. Pt key to "ON", put fan on low, press A/C button in. You should hear a noticable click coming from outside
motor on----> same procedure only listen for the rpms, if it fluctuates (usually down) chances are it's grabbin, look at the pulley's balancer and verify.

If it is not engaging check the fuse, gas level, and wiring for shorts etc


A/C cools very little
1. over/undercharged system
2. make sure both fans work (at least the condensor fan should come on when you kick on the a/c)
3. kinked lines


If your a/c hasn't worked in a while don't worry, it CAN be resurrected, here's how I did mine
1. removed all a/c components and flushed using powerful solvents
2. replaced damaged/missing lines (junkyard)
3. replaced all seals (only about 10 of them total, new from my mechanic)
4. new expansion valve and reciever/dryer (Honda)
5. junkyard compressor (a reman. would be nice)
6. condensor fan

after a fiasco with a halfassed job by a shadetree mechanic I sucked it in and saw my real mechanic and asked him what I should do. He started off by showing me this black shit was oozing through the system and he said I need to start by taking it apart and flushing it out (he provided the flush) and cleaning all the fittings. All fittings got fresh seals with esther oil to keep them soft and I flushed out the compressor with mineral oil (to save $, it's only to get the black stuff out that came from the junkyard condensor) and then again with the esther oil. Put her all together and drove to the mechanic to get it charged. About $250 later I was chillin with COLD A/C

[AZmike]

Originally posted by POS carb
You get water pump it through the motor and radiator, fans pull air over the radiator fins and cool the hot fins (which have become hot by drawing kinetic energy from the water) and in turn cool the water, which gets pumped back into the motor to draw heat off the head. Rinse. Repeat.

Did you mean 'thermal' energy rather than 'kinetic' or were you talking about the increase in movement at the atomic level associated with an increase in temperature?