Summer time troubles

[spacecadetz26]

Q
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How do you guys get these things so screwed up.....

Compressor take the cool low pressure gas and makes it high pressure, then the condensor takes the excess heat out of the gas (now liquid) using the outside air (fan) and passes the liquid through the accululator/filter/dryer and then it goes through the expansion valve.  When the high pressure liquid squeezes through the small valve it expands rapidly into a low pressure area.  This is where all the cooling potential is.  This area is commonly known as the evaporator.  Then after the gas is heated some (by cooling the hot air in the car, which cools the cabin air and makes cabin colder) the now expanded and somewhat warmer gas goes back to the compressor to be compressed again into a liquid.

This is a VERY simple but accurate discription of the flow path, unlike the first post.  Why would a compressor make a high pressure into a lower pressure?  Then what would you do with it and how could it make anything colder???  Basic gas laws phrohibit such actions. ÂÂÂ

Read this if you have more questions.  It covers the basics fairly well.

http://home.howstuffworks.com/ac.htm




in auto a/c the refridgerant never goes into a liquid state. its either high pressure or low pressure/ high temp or low temp gas. while freon does have some water "vapor" in it, should never be confused with a liquid.

added: the accumulator/reciever-dryer takes the moisture out of the gas using dessicant or acts like a dehumidifier.

[rweatherford]

Hmmm...  never a liquid state eh?

It's been a long time since I have had a class on thermodynamics with state changes, but I'll give it a shot.

If I read this chart correctly....

http://www.wsconet.com/Pressure%20Chart.htm

Then @ 80 deg F R-12 has a vapor pressure of 84.1 in Hg. above 1 ATM.

On your gauge manifold the reading for a liquid state of R-12 would be only 41 PSI.

Granted the ouput temp of a compressor is more like 150 + degrees but I bet the temp after the condenser is close to ambient + 20 degrees.  So we might say it is 120 degrees on a hot day.

That takes about 77 PSI on the high side to create liquid.  Anything below this creates vapor.

Generally the high side pressures run from 150-250 PSI and the low side is from 45-25 PSI.  Just enough to make the liquid turn to a vapor a create a very cold spot in the evaporator (generally just above freezing).

Please correct if these items are not true.

R-134a has a slightly higher vapor pressure and is why it does not cool as well unless the expansion valve is designed for it.

[spacecadetz26]

here's a good one for you rex.

Where is the expansion valve/ orifice tube on a Beretta's A/C system?

[rweatherford]

On the evaporator under the dash.  The thermal bulb is attached to the outlet of the evaporator.

[Guest]

I am not sure what it's called but I know a local used car dealer that can sell me a product that works in -he says either system-
I know it works  in the older r12 systems-last time i bought a can it cost me somewhere around 9 dollars a can.It may not get as cold as the stuff you mentioned though,since I didn't measure it
  The 94 should have a 134 system --i Know my 94 does.

[Guest]

hey-is this the correct place to post an a/c question and problem?I want to be sure before i post it.  

[Jeff P]

The 'Diagnostic Help' section would probably be better unless you think it might be a very commonly asked question.

[blackedz26]

ok, so my question is, where is the nozzle you put the recharge in? on the underside below the fan? after the compressor has protected itself, after it has been recharged,, will it re start itself?