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Old 08-01-2013, 02:09 PM   #1
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Default A/c 101

Hi I am a certified tech of over 20 yrs. A lot of people have been asking me, and I have seen in various forums, people asking about A/C systems. So I decided to try and take some mystery out of the game.
A/C systems work on the principal of heat transfer. Hot always goes to cold. Think of a glass of ice cold lemonade in the summer. The outside of the glass gets wet from the heated air moving to the cold glass condensing and depositing its moisture on the glass. And thusly warming the lemonade. Instead of a glass if you were to fill a tiny radiator with the same lemonade and put a fan behind it you would notice the air is cooler. Basicly that's how an A/C system works.
The automotive A/C system has only a few components . The compressor, it compresses the r134a raising its boiling point. The condenser, cooling the compressed r134a. The high pressure switch, which shuts off the compressor if the system is way over charged. The acumilator, which removes residual moisture in the system. The low pressure switch, which shuts off the compressor if the system is low. The evaporator, which allows the aforementioned heat transfer. And the oriface tube, which collects debris that could damage the compressor. The electrical side of the system is easy. Power comes from the fuse box to the A/c switch on your dash, then to the A/C clutch relay. From there it travels through the high pressure switch, then the low pressure switch, then to your A/C clutch ( on the front of your compressor) then to ground.
The A/C system is a " sealed " system. So if you are low on R134 you have a leak that needs to be repaired. However the rubber in the lines of the A/C sys are porous, like your tires. Over time they leak. That is one of the reasons for the oil in the system. The oil is there to lubricate the components of the system and coat the systems hoses to help seal them, kinda like fix a flat Coates the inside of a tire to fix a small puncture.
When A/C systems fail it's mostly due to a leak, faulty compressor, or an electrical issue. Most, not all, but most occur at the condenser in front of the radiator. Due to the fact it picks up the road debris and gets punctured. The compressor usually fails due to a worn out clutch or debris in the system that fails the internals of the compressor. On the electrical side its usually a fuse or the A/C clrtch relay.
At work I have an A/C machine to use. They usually run a few grand! Next post will be how to diagnose and charge your system at home. Hint leave those " do it yourself kits" for the noobs!
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Old 08-02-2013, 10:47 PM   #2
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Old 08-06-2013, 04:08 PM   #3
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OK so your A/C system isn't working. The tools you need can get a little expensive, but once you get good you can charge your friends! You'll need a test light, a paper clip, a r134a gauge set, a UV light, a vaccum pump, and a air compressor. The compressor you can possibly borrow and the other tools you can get at a good parts store for about $175.00 or so.
So let's get started! Step 1 start your vehicle turn on the A/C and see if the compressor is engaged. When engaged the center will turn, when not engaged only the belt turns on the pulley. If your compressor is turning, even intermittently go to step 3, if it's not turning go to step 4.
Step 2 Shut the engine off and turn the key to the on position with the A/C is switched on. Disconnect the A/C low pressure switch. It's usually on the right side of the engine compartment near the accumulator. Get you test light and test the connector. You should find power on one pin and ground on the other. No power, the check your fuses and relays and go back to step 1. Power no ground go to step 3
Step 3 install a paper clip in the connector you should hear the compressor clutch click if you do go to step 4. If not check the connector on the A/c clutch. You should have power on one pin and ground on the other. If you do your compressor is most likely shot. If you do have power but no ground, or ground but no power repair your wiring and go back to step 1.
Step 4 We've now verified the system electrics and the compressor, so we're probally low on r134a which means a leak. Hook up your gauges and start the engine. A fully charged system should show about 40 p.s.I. on the blue hose (low side). If its less than that we know we have a leak connect your vaccum pump and evacuate the system. Bring the system down to 20+ hg and hold. Watch your gauges whichever on rises faster gives you an idea which side the leak is on....high side or low side. And the speed that the system looses vaccum gives you an idea how bad of a leak you have. However you can have a leak and still pull and hold a vaccum, so go to step 5
Step 5 Buy two cans of r134a with UV dye in it. Not the recharge kits they sell over the counter. Generally they contain additives and sealants that can harm your system over time. In minor amounts no problem, filling a system and you could have issues. Charge your system to manufacturer specs. Once charged use you UV light to check each connection, line, and part for signs of the UV dye. Find the dye (which will show a yellowish/green flouresent color under the black light) and you found the leak. I like to use a sniffer for this as it gets into areas you can't see. However they alone can run $150.00 and up. At this point your system should be working. Depending on how bad your leak is, it could last a few days to a few months. Now you can vaccum the system and repair or replace the leaking part or parts and go back to step one. Or run it till it runs out then go back to step 1
Few rules 1 Never open a charged system, always verify the system is empty before disconnecting any lines. 2. Don't overfill the system, this can lock up the compressor. 3. Only fill the system to manufacturer specs. Under filling or overfilling WILL damage the system. 4 Be aware of the fan and moving or hot parts.
This is a general approach to repairing your A/C system in your back yard. Just a guide not a rule.
Questions? Comments? More info?
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