compressor turns on and off

snksknr said:

Yes I was using a cheapie gauge from auto zone, I figured that might have been good enough. I guess I'll start with the A/C pressure cycling switch. Thanks.

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Brock94 said:

Before you start replacing parts, don't jump to any conclusions-- you still haven't ruled out the possibility of a low charge or a clogged orifice tube. Even though the cheapie gauge reads pressure in the "green" zone when the system is off, it doesn't mean there's an adequate charge. An A/C system is not like a tire that you just fill to the right pressure. When the system is off, A/C refrigerant will exert the same amount of pressure with 1/4 charge as it will with a full charge.

Since you are trying to avoid a costly repair and you don't want to make your system any worse, why not invest in a manifold gauge set for about $40-100. Then you can read your pressures with the system running and we can tell you more about what might be wrong.

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davidmmm69 said:

someone who knows nothing about the AC system. surely doesn;t need a set of manifold gauges. to get him in further trouble.

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A clarification regarding how our air conditioners work.

The orifice has a hole in it. There is liquid on one side and pressure forces the liquid through this tiny hole which vaporizes it, something like a sprayer on the end of a garden hose.

When liquid is changed to a vapor like this a miracle occurs, it absorbs heat. This is why the evaporator follows the orifice, blowing cabin air through the evaporator transfers the heat to the expanding vapor inside the evaporator. Out of the top of the evaporator is low pressure gas.

The low pressure gas, and any suspended liquid refrigerant, goes to the accumulator, where any remaining liquid falls to the bottom leaving only low pressure gas. This is where the LP port is.

This low pressure gas is compressed by the compressor into ..... hot high pressure gas. Through the muffler and to the condensor. Just before the condensor is the high pressure port. At the condensor another miracle occurs, blowing air through the condensor removes the heat from the hot HP gas and turns it into a liquid. This is the liquid at the orifice that started this. So the orifice is the device that provides a difference between liquid and vapor. I'm too lazy to look up the thread with a pic that describes this.

A new bad compressor isn't as unusual as it should be. You may be able to return it, no doubt they will ask you if you repaced the accumulator and the orifice, it's generally in the warranty small print. Common cause for failures in new compressors is insufficient oil or crud from the system. And sometimes, as in your case, **** happens. I distrust the Chinese rebuilds.

Good Luck!

Posted by: shamaal

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What's wrong with my Air Conditioning?
A number of things can happen to make your A/C quit working. Here, we'll go over some of the common problems, and what you can do to fix it.

Leaks / Low Refrigerant
No A/C system is completely, 100% sealed. Over the years, small refrigerant particles will leak out, up to 1/2 ounce per year. On smaller-capacity systems, this will become noticeable a lot quicker than a larger capacity system. In this case, the most practical thing to do is simply add a bit more refrigerant. You will want to hook up a set of manifold gauges to make sure that the system has at least some pressure in it before you add refrigerant, because if the system is completely empty, you might have a most severe leak. At best, you will still have AIR in the system, and you want NO air in there.
Symptoms of low refrigerant include rapid cycling of the compressor clutch, or clutch will not engage, little or no cooling, very oily spots on A/C components.
A severe leak will require repair or component replacement. To find a leak, there must be some refrigerant in the system. An electronic 'sniffer' or dye are the most effective ways of finding a leak. Most A/C shops can perform this service for a minimal charge. Some retail auto parts stores also loan or rent tools for this.
Once the leak is identified, the component should be repaired or replaced, and the system serviced.
*Tip* - Evaporator leaks can be difficult to find, since the evaporator is usually not easily accessible, located in the dash of the vehicle. With dye in the system, place a white, preferably unused baby diaper under the evaporator drain tube. Moisture will drip on to the diaper. If there is dye in there, you'll know it!

Poor Airflow
One of the most-missed problems is poor airflow. Your A/C comes on, but it's not very cold. If you have a gauge, the high side pressure seems awfully high.
There are a couple of quick, easy things to check. First, make sure the condenser is debris-free, and that the fins are not all bent over. The condenser is located right in front of the radiator. Bugs, rocks, plastics bags, etc. covering the front of it prevent air from passing through, cooling not only your radiator, but also the refrigerant in the condenser.
All engines have either a fan clutch or radiator / condenser cooling fans. Fan clutch go out all the time. The fan clutch is located between the radiator and the engine, and has a big fan blade attached to it. With the engine on, that fan should be turning very fast, and moving a lot of air, TOWARDS the engine. Running correctly, you will not want to get your fingers near it. I recently repaired a 1996 Chevy truck that had blown the compressor shaft seal. While diagnosing the system, I noticed that the fan was barely turning. I could actually stop it with my hand. (not recommended for the non-professional) Because there was poor airflow, the pressure (pressure is temperature) built up from the condenser to the compressor, and was more than the compressor shaft seal could handle.
If the vehicle has an electric fan, make sure it (or they) comes on, and that the air is fast, and moving TOWARDS the engine. If the fan(s) does not come on, check the fuse. If that's not it, you may need to replace the fan.
*Tip* - You can confirm proper airflow by TEMPERATURE TESTING. A good thermometer that can be touched to the inlet and outlet of the condenser will confirm proper airflow. You should see a 20 to 40 degree drop from the inlet to the outlet of the 2 condenser pipes. For example, if you measure the temperature at the inlet (where it comes from the compressor) and have a temperature of 160 degrees, the outlet should be 100-140 degrees. Less than 20 degrees difference usually indicates poor airflow. MORE than 40 degrees usually indicates a restriction in the condenser.

Restrictions
A restiction is a condition where some piece of debris has lodged in a component, and is 'restricting' the flow of refrigerant. Condenser restrictions are the most common. Most late-model condensers have very small passages, as low as 6mms! When there is a restriction in the system, the flow of refrigerant is greatly slowed, or sometimes stopped completely. The blockage causes pressure to build up behind the restriction, and will cause damage to the components behind it.
The most effective way to locate a restriction is with temperature testing. With a good thermometer, temperature (which is pressure!) can be measured ANYWHERE on the system. Large drops in temperature can be identified and repaired. For example, a restircted condenser...If the inlet measures 160 degrees (about 295 psi) and the outlet measures 90 degrees (about 103 psi), it means the refrigerant is slowly leaking past a restriction. Because the refrigerant spends more time in the condenser, it has time to cool of more. Problem is, that 295 psi will continue to build back, and will eventually blow a seal somewhere, probably in the compressor.
Some restrictions can be repaired by flushing the restricted component, but parallel-flow condensers usually need to be replaced.

Improper Refrigerant Charge
As A/C systems become smaller and smaller, the amount of refrigerant in the system becomes critical. The correct charge for an A/C system has been calculated and engineered by vehicle manufacturers for optimum performance. Here are some tips to keep in mind when charging a system:
Charging with cans: A 12 ounce can of refrigerant gives you 12 ounces of refrigerant, right? Well, not always. If you are using a gauge set to charge, those hoses can hold up to 4 ounces of refrigerant themselves. On a 56 ounce capacity system, those 4 ounces might not make a big difference, but on a 1 pound system, you can bet it will. Also, notice how when you pull the can tap off, how the can wasn't quite empty? Yep, another ounce or 2 there.
Too much! Your A/C isn't quite cooling, so you run down to the parts store or a big box retail store, and buy a recharge kit. We in the industry call 'em suicide kits. You add a can of refrigerant. Well, with A/C, too much isn't better.
Retrofitting: Vehicles manufactured prior to 1993 and some 1994 originally came with R12 refrigerant. Because of the cost of that refrigerant, most folks opt to retrofit to R134a refrigerant. Problem is, there is no set standard for how much R134a refrigerant to use in an R12 system. There are many misconceptions about how much to use, and some people have come up with percentages of original charge. I've heard to use as little as 60% of the orginal charge!
So how do I know if I have the proper charge? Our old friend temperature testing can help determine if you have the proper charge. Orifice tube systems are the easiest and most accurately confirmed systems. It can be done on expansion valve systems, but you'll need to get on the evaporator side of the expansion valve.
Here's how: Measure the evaporator inlet pipe and record your temperature. Now measure the outlet pipe of the evaporator. Those 2 temperatures should be as close to equal as possible, at least within 5 degrees of each other. If the outlet is MORE than 5 degrees warmer than the inlet, you still need more refrigerant. If the outlet is MORE than 5 degrees cooler than the inlet, you have too much refrigerant in there.
Final tip: If your A/C is working, don't mess with. If you have an R12 system, you do NOT need to have it converted to R134a just because someone tells you that R12 is gone. If it's working, leave it alone.
If your system is working and sealed, you DO NOT need to replace your filter drier or accumulator. This is not a part that wears out. The only time you need to replace it is when the system is opened, or if you've had a leak that allows air (and moisture) into the system. If someone tells you you need to replace it every 3, 5 or 7 years, they're trying to sell you something.

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AC Work - Caution:

This is really just a safety thread for you DIYs. A/c systems can be easy (sometimes- with the right tools) to work on, but you must be careful around the stuff. Through those lines and in the compressor is highly compressed gasses/fluids and you need to understand that they are heavily pressurized. Even when you pull vaccum or pull the system down, STILL take precautions when taking lines off.

ExplorerDMB

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I ALWAYS recommend wearing eye protection when working on a charged system and fooling around with fittings etc. Refrigerant in your eye isn't a potential problem later, it is a certain BLINDNESS or serious vision problem RIGHT NOW ! Corneal replacements are not fun, cheap, nor easy to come by. Safety glasses may not be fun but they are cheap and easy to come by. Blindness sucks.

Glacier991

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Evacuate and Charging Procedure.

Attach a/c manifold gauges to the vehicle. Make sure you attach the correct hose to the proper service port. This is very important to prevent personal injury! Attach center (Yellow Hose) to a UL approved a/c vacuum pump. Open both of the dials on you’re a/c manifold gauge set. This will allow the system to be evacuated through both the low and hide side of the system. Turn your approved vacuum pump on starting the evacuation process. 30 minutes usually will be enough time. If vacuum pump has ballast read the owners manual concerning this option.

When system has achieved a state of 29.9 hg’s of vacuum close both dials on the a/c gauge set. You may loose up to 1 hg for every 1000 feet above sea level depending on the capacity and quality of pump. At this point wait 5 to 10 minutes letting the vacuum boil off any moisture trapped in the refrigerant oil. This is also a good time to watch and see if vacuum has returned to a zero state. If so you need to check for leaks in the system. Assuming the system is holding a vacuum after letting the moisture boil off repeat the evacuation procedure again. This process may need to be done a few times before all moisture has been removed and you see no degradation in vacuum after closing both dials for 5 to 10 minutes.

With both dials closed remove the center charging hose attached to the vacuum pump and connect it to either a can tap and refrigerant or 30lbs refrigerant cylinder. Open the valve on either the can tap or 30lbs cylinder allowing refrigerant into the charging hose. With refrigerant in the charging hose slowly crack this hose at the manifold gauge bleeding off any air that may have gotten trapped when moving from the vacuum pump to the refrigerant source. Only the slightest amount of refrigerant should be released in this process so be sure to tighten the charging line quickly!

Open only the low side dial on you’re a/c gauges allowing refrigerant to flow into the system. Again I stress the high side must be closed or you may cause personal injury to yourself or others! Start vehicle and turn on the a/c system with blower on the highest speed. In some cases if the compressor clutch has not engaged you may need to by pass the low pressure cut out/cycling switch. Refrigerant should be charged as a gas but in some cases it may be necessary to charge as a liquid. Be careful not to slug the compressor with liquid refrigerant! Charge system to OEM amounts and pressures if you are using the refrigerant the system was designed for. If vehicle is has been or is being converted start with about 60 percent of the original charging amount. After getting 60 percent of the original charge slowly add an ounce at a time until you reach the best possible vent temperature and pressure readings. If you do not know what your systems operating pressures are you can use the 2.2 x the ambient temperature as a guide. This should only be used as a guide as many systems will need more or less refrigerant to achieve proper cooling.

Having a weak fan clutch or an inoperative electric fan will cause system pressures to be incorrect. So make sure these components are working correctly before charging a system!

In lower ambient climates, doors and or windows of the vehicle maybe required to be open to achieve proper cooling when charging the a/c system.

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First, you still have air in the system because you must use a separate vacuum pump and its not evacuated completely down until you get to 29in. vacuum. Running the compresser with out r134a is like running your engine without oil.
Second, If you didnt remove any oil you shouldnt add any. Over oiling reduces the efficiency of the system. You must drain the compresser of oil and put back the same amount.
Third, Overcharging is murder on the compresser and will soon fail.
Fourth, The proper way to check the system is to check the ambent temp chart and run the fan on high cooling at max and no recirculate. With a long stemmed thermostat check the outlet temp at the RH passanger outlet with engine at idle for at least 10 minutes running and compair it with the chart temp.
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Shamaal said:

The switch on the accumulator controls the clutch on the compressor. When the system pressure is less than 24.5 psi the clutch is disengaged. When the pressure is greater than 43.5 psi the compressor clutch engages. The switch is screwed on to a schraeder valve, like on tires. It can be removed without discharging system, having said that there have been two instances this season of sticking valves. Running the compressor (jumpering) without oil for >30 seconds can damage it.

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AC Clutch won’t shut off:

Juice to the compressor is controlled by a relay which is driven (grounded) by the PCM. The low pressure switch sends a voltage signal to that Relay. When the contacts are open, there shouldn't be any voltage on the output side of the switch. Take your meter and probe both sides of the harness. Lt Green seems to always be the input and Blue or White (or whatever the line felt looked good the day it was built) the Relay signal. If you find voltage on both, there's a short between the Pins or that output is picking up voltage from somewhere else. If no volts, you can spend 9 Bucks on a new relay, but you might remove it first and see if the compressor continues to run. If it does, the clutch wiring is shorted to a voltage source.

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