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Q: There’s no cold air but I can hear my compressor coming on.
A: There could be several reasons why your A/C compressor is coming on (or cycling on and off) but you still do not have cool air coming from the vents in the car. The reason is that the A/C system is under a superheat condition. That means there is not enough liquid refrigerant in the A/C evaporator to effectively transfer the heat.
The superheat condition is caused by only one of two reasons. Either there is a problem with the refrigerant flow that is restricting the amount of refrigerant entering into the evaporator OR the system is low on refrigerant and there simply is not enough to maintain the proper liquid level in the evaporator.To test, add a small amount of refrigerant (usually between 2-4oz.). If the added refrigerant corrects the problem, you most likely have a leak and the system should be recovered, have the leak repaired, install a new filter/drier or accumulator and the proper amount and type of refrigerant oil and vacuum and recharge the A/C system with the original factory specified amount of refrigerant. If the added refrigerant did NOT improve the cooling, you most likely have a restriction within the A/C circuit. That could be at the condenser, drier or expansion valve or orifice tube. The system will have to be diagnosed in order to determine the real problem.
Q: Can I cause damage if my A/C system isn’t blowing cold air and I continue to operate it?
A: YES! You can cause damage to an A/C system that is working (or has the A/C compressor engaged) but is not blowing cold.
The biggest problem is that your system is probably low on refrigerant. When that happens, your A/C compressor is not being cooled properly. The same refrigerant that keeps you cool also cools your compressor. Without the proper flow of refrigerant, your A/C compressor isn’t getting proper lubrication. That’s because there is not enough refrigerant flowing through the system to carry the required amount refrigerant oil to the A/C compressor. That can quickly cause catastrophic failure.If this is happening to your car’s A/C system, leave your A/C controls in the OFF position until the A/C system is diagnosed and serviced. That way, you are not calling for the compressor to engage and you will reduce the risk of having a catastrophic failure (See Catastrophic compressor failure post in this “How To” section)
Q: The air doesn’t blow out of the right vents but my A/C works.
A: This problem lies in the controls that regulate the air distribution. The refrigerant circuit only provides the means to remove the heat from the air entering your vehicle. The control system handles the air distribution so that you can select the dash, defrost, floor vents.
Sometimes the air distribution controls operate with manifold vacuum. This is vacuum created by your car’s engine. Your A/C system uses a canister or reservoir to save vacuum and operate the blend and air control doors.In a lot of cases, when a vacuum line under the hood is broken or not replaced (sometimes during other automotive services), you loose the ability to control the air distribution. The typical failure is that all the air is coming out of the defroster or the floor. Those are usually the ‘defaults’ for the system. In order to correct the problem, you simply have to find and repair the vacuum leak.
Although that sounds easy, there are a lot of different vacuum lines under the hood of any vehicle. Vacuum lines are typically small (about 1/4″ diameter or less) hoses that are routed from the engine. They can get loose, cracked or even get holes from hot exhaust manifolds. The actual vacuum reservoir can leak. It can be located anywhere under the hood, but typically on the passenger side near the firewall. Check the hose connections and the canister itself. Leaking canisters shouldo be replaced, but they are usually not expensive.
Q: Where are the charge ports on my A/C system?
A: Your auto A/C system includes 2 charge ports. One for the low side and one for the high side. The simple way to find them is to trace the lines. Usually, from the evaporator outlet, (near the firewall) follow the line to the A/C compressor. The LOW side port should be on this line. For systems using an accumulator, it may be one of the ports right on the accumulator. To locate the HIGH side port, locate the A/C compressor. Follow the line that goes to the condenser (usually the smaller of the two). The HIGH side port may be on the line between the compressor and the condenser OR it could be on the line after the condenser; between the condenser and the evaporator inlet. On R-134a systems, the HIGH side charge port will be larger than the LOW side port, and will require quick connect fittings to connect. If you are using a set of R-12 gauges, don’t worry! You can convert those gauges to work with R-134a! Check an auto A/C system illustration to help you locate the charge ports.
Q: When should my A/C system be serviced?
A: Your auto A/C system is a closed and sealed system and should not require regular service or recharging unless the system is being opened for service. However, the system does leak (over time) because there are no seals that are 100% leak free. You should also know that compressor shaft seals require lubrication with refrigerant oil in order to hold their seal and will leak when the A/C system is not operated for extended periods of time (Fall, Winter and Spring). As long as your A/C system is cooling properly, there is no reason you should have to have it recharged. If you find that it is not cooling as it should you need to have it checked and serviced and it will most likely require recharging. For information on how to recharge your A/C system check the A/C Charging post in the “How To” section here . Keep in mind that if you continue to operate a system that is not cooling properly it could cause sever damage to your A/C compressor! How can you tell? Just have a look at your orifice tube. Every orifice tube will tell a story about the condition on your A/C system. When your orifice tube is restricted, you have a serious problem that requires immediate attention and your entire A/C system should be flushed!
Q: What equipment do II need to recharge or service my auto A/C system?
A: The basic equipment that you must have is a set of gauges that include charge hose and couplers or adapters to connect to your a/c system and a vacuum pump. Safety glasses and work gloves are also important because refrigerant can cause serious bodily harm!
Q: Does more refrigerant make the A/C system colder?
A: No! In fact, the charge capacity of any a/c system is specific and all efforts should be taken to be sure that the system is charged with the correct amount of refrigerant. That’s why ‘topping off’ an a/c system is really not recommended.
Q: Can I just top off an A/C system that’s low on refrigerant?
A: The problem is that you can never tell how much refrigerant is in the system before you start to top it off. You test and diagnose A/C system using manifold gauges. They provide a pressure reading. That pressure reading is in no way related to the amount (weight) of refrigerant in the system. Therefore, you can never be sure of how much is already in the system. Above that, late model vehicles now have a full spec charge of just several ounces (as opposed to older applications that were between 3 and 4 pounds of refrigerant). If the total charge is 20 or 25 ounces, being ‘off’ by 4 or 5 ounces could be the difference between cooling and no cooling. You should always recover the refrigerant in the system, pull deep vacuum for at least 1/2 hour (to remove air and moisture) and recharge with the full factory specification refrigerant charge.
Q: Can pressure gauge readings tell me how much refrigerant is in the A/C system?
A: No. The pressure gauge readings can not tell you how much refrigerant is in your A/C system. That’s because you charge an A/C system by weight of refrigerant, not by pressure. The typical auto A/C system may have a full factory spec charge of 1 pound and 10 ounces or 26 ozs. The pressure gauge readings only tell you what the pressure of the system is. The pressure gauge readings will change depending on the ambient temperature of the day. This is because the refrigerant has a pressure/temperature relationship. If the ambient (or outside) air temperature increases, so does the pressure within the system.
Q: How do I know if my auto A/C system is low on refrigerant?
A: There is no easy way to tell if your A/C system is low on refrigerant. The pressure gauge readings indicate the pressure within the system, not the amount of refrigerant in the system. Therefore, connecting a set of pressure gauges and taking a pressure gauge reading will not tell you that the system is low on refrigerant. However, you should know that experienced A/C service technicians generally understand what the pressure should be. With that experience, they can quickly test for low refrigerant charge by adding a small amount of refrigerant (usually between 3-4 oz.). This is a common practice when diagnosing the auto A/C system. By adding the refrigerant, the service technician is trying to see if the pressure gauge readings improve. If they improve, then the small amount of refrigerant confirms that the system was low. If the pressure gauge readings do not improve with a small amount of refrigerant added, there are other problems or restrictions in the A/C system.
Adding refrigerant to an A/C system is not legal in some places. Adding refrigerant for ‘test purposes’ only, usually between 3-4 oz., is adequate to determine if the A/C system is low on refrigerant. Almost all places allow for small amounts of refrigerant to be added for testing.Q: How can I tell if my A/C system is overcharged?
A: There is no fast and sure way to determine if your A/C system is overcharged. Some of the symptoms are that pressure gauge readings will be high (on both the high and the low side), and the cooling performance will be poor. But like an undercharge condition, pressure gauge readings can not give a definite answer. The only way to know if the system is overcharged is to recover all the refrigerant, vacuum the system and recharge the system with the full factory specified amount of refrigerant.
Removing, venting or adding refrigerant to an A/C system may not be legal in some places. Any refrigerant should be recovered into a refillable container manufactured for the purpose of storing refrigerants. It should be EPA compliant.Q: Does the A/C system have to be vacuumed before recharging?
A: Yes, the A/C system should always be vacuumed before recharging. Vacuum removes air and moisture from the system. Moisture creates harmful acids when mixed with the refrigerants. Acids will corrode the system internally and can cause restrictions at the orifice tube. Air causes problems with high pressures and is very difficult to diagnose when it’s in an A/C system. The air is considered a contaminant and is a ‘non condensable’ Therefore, it will be trapped at the top of the condenser. The only sure way to remove the air is to vacuum the system before recharging, and always be sure the hoses on your gauge set are purged of air.
Q: How does air get into the system when I am recharging or adding refrigerant?
A: Typically when recharging the A/C system, the system is vacuumed, and you will not get air into the A/C system. However, when adding refrigerant or ‘topping off’ the A/C system, you can easily get air into the system right from the hoses on your gauge set. Before connecting to the system, if your gauge set hoses do not have refrigerant in them (being held by the quick couplers) then they are full of air. Connecting them to your A/C system and then adding refrigerant or freon will cause the air to be pushed into the system. Longer charge hoses create a bigger problem. To eliminate this, simply ‘purge’ the hoses. That’s done by ‘cracking’ the hose at the threaded connection. Usually opening that connection about 1/4 to 1/2 turn will cause refrigerant to leak. Once you’re leaking refrigerant, you know you have the air removed or purged from the charge hose. You’re ready to add refrigerant.
Q: What kind of vacuum pump should I use??
A: It just has to be able to pull deep vacuum in order to boil moisture and remove the air that may be in the system. When you’re deciding on a vacuum pump, you should pay more attention to the ‘micron’ rating. That’s the level of vacuum that the pump is rated for. The lower the number, the better the pump. Water only starts to boil at levels of vacuum under 1,500 micron. Deep vacuum is typically at levels under 750. You should really aim for 500 microns or under. The most popular type of vacuum pump is the rotary vane design.
Q: How do I vacuum the A/C system?
A: In order to vacuum the auto A/C system, you need a standard manifold gauge set and vacuum pump. Start by being sure that all control valves on the gauge set are closed. With the pressure gauges connected to the A/C system (red hose to high pressure side and blue hose to the low pressure side) connect the yellow (center hose) to the vacuum pump. Start the vacuum pump and then open both high and low side control valves on the manifold gauge set. This assures that vacuum is being pulled throughout the A/C system.
Typically vacuum is pulled for about 1/2 hour, but that will depend on the condition of the system and the work being performed. In the case of regular maintenance, a 1/2 hour vacuum at 29.9″ should be fine. Where a system has been contaminated or suffered catastrophic failure (ie.: seized compressor) it’s generally a good idea to vacuum for at least 1 hour or more to assure a totally dry system.It’s also important to assure that your vacuum pump pulls deep vacuum. Water does not boil until the level of vacuum is under 1,500 microns. Deep vacuum is considered to be under 750 microns. Ideally, for automotive service, you should attain at least 200-300 micron vacuum if not lower.
Q:How do I find the orifice tube on my A/C system?
A: The orifice tube will always be in the liquid line between the condenser and the evaporator inlet. Typically, they are installed right in the inlet of the evaporator. However, on more current model vehicles they may be in the A/C condenser outlet or actually ‘in-line’ between the condenser and the evaporator.
Q: Why is the location of the orifice tube changed on some vehicles?
A: The orifice tube is a fixed opening. When the A/C system shuts off, both sides of the system will equalize through the orifice tube. When that happens, there is a definite ‘hissing’ sound. Because that sound can be heard inside the passenger compartment of the vehicle, it was decided to move the orifice tube further up the liquid line (on some vehicles) to reduce the noise.
Q: Does the orifice tube have to be installed in a specific direction?
A: Yes! The orifice tube does have to be installed in a specific direction. Simply speaking, there is a ‘long’ and ‘short’ screen on each orifice tube. The ‘long’ screen is the INLET filter. Therefore, it should be at the inlet side (from the condenser). The ‘short’ filter screen should be pointing towards the evaporator (or outlet of the orifice tube). Also, if you look closely, there is usually a flow arrow that will show you the proper direction of flow through the orifice tube. It’s in the plastic portion of the orifice tube. That will tell you what direction the refrigerant is expected to flow through the orifice tube.
Q: What about TXV’s or expansion valves? Can they be checked?
A: The answer really depends on which type of expansion valve your auto A/C system has. The typical type expansion valve that has an external capillary tube (where the sensing bulb is usually attached to the evaporator outlet) can be tested. The test process is to remove the sensing bulb (gently). Use caution so that you do not ‘kink’ or bend the tube. With the A/C system charged and running, FREEZING the sensing bulb should cause the low side pressure to rise over 45 p.s.i. WARMING the sensing bulb should cause the low side pressure to drop to zero and possibly vacuum. For a valve to be considered ‘good’, BOTH pressure gauge reading conditions must be met.
Q: Do I have to add refrigerant oil to the A/C system when I recharge?
A: The general rule is that the automotive A/C system is a closed system, and unless oil has leaked out, there should be no reason to ‘just add oil’ every time you recharge the system. Having said that, it’s also true that components like compressor shaft seals and some ‘quick connect’ fittings will leak oil and may not even show a sign. Adding an ounce of refrigerant oil to an otherwise leak free system is not going to hurt it. Just don’t add too much because an oil overcharge can cause poor cooling problems.
Q: How much refrigerant oil should I add to the A/C system when recharging?
A: There may not be a requirement to add oil to the A/C system every time it’s recharged. However, if the system requires oil, you should only be adding the amount of oil that’s been lost. With leaks or ‘normal’ loss of refrigerant oil through the a/c compressor shaft seals it may be difficult to determine exactly how much to add. Therefore, you should follow the general ‘rules’. Adding 1-2 ounces for loss through small leaks or through the compressor shaft seal is acceptable. When replacing components, there are additional guidelines that should be followed. They are; A/C Condenser – 1 oz.; Accumulator or receiver drier – 1 oz.; Evaporator – 3 oz.; Compressor – Generally, the amount removed plus one ounce (1oz.). For more detailed refrigerant oil specifications, follow the Factory Service Manual for your specific application.
Q: When adding refrigerant oil to the A/C system, where do I add it?
A: There is no hard and fast rule about where to add refrigerant oil to the automotive A/C system. If you are replacing a component (like an accumulator or receiver drier) the refrigerant oil can be added right to the part. Simply measure the required amount and pour it into the part before installing it. If you are adding to a closed system (where no parts are being replaced), you will need to add the refrigerant oil using an oil injector or you will have to open the system to pour it in. Typically, the best place to add the oil would be to the low side of the system. Refrigerant oil will circulate throughout the system and ‘seek’ it’s own level once the system is operating.
Q: What if I am replacing the A/C Compressor? Where do I add that oil?
A: You should follow the instructions provided with that compressor. Some compressors will ship to you with the oil already installed; others will ship almost dry. If no manufacturer’s instructions are available, start by draining all the oil from the new replacement (or reman replacement) and from your old compressor. Measure the amount drained from your old compressor and add that amount plus one ounce to the replacement. That oil should be added directly into the suction port of the A/C compressor. If you can not drain any oil from your old compressor, you should add about 1/3 of the total system charge of oil to the compressor. The A/C system should hold between 8-12 ounces of oil. Therefore, depending on your particular system, you would add between 2-1/2 and 4 ounces into the replacement compressor.
Q: Can I replace an A/C hose using fittings and hose clamps?
A: No, on older R-12 A/C Systems, hoses used what was known as a “Three Ring Barb” style fitting. With those fittings, you could install a new piece of hose and utilize a standard ‘worm gear’ hose clamp to secure the hose. On current auto A/C systems using R-134a refrigerant, all hoses are barrier type A/C hose. Three ring barb fittings should not be used on barrier hose because the barbs pierce the inner nylon core of the hose, causing it to leak prematurely. All R-134a systems should use barrier hose and proper ‘bead lock’ fittings. Those fitting incorporate the crimp ferrule (or shell) into part of the fitting, and they will have to be crimper using a A/C hose crimper.
Q: How do I measure the fitting or hose on my A/C system?
A: Always determine the fitting size by taking a measurement of a straight section of the tube, as close to the hose section as possible. You will find that typically, auto A/C tube sections are 3/8″, 1/2″, 5/8″ or 3/4″ in O.D. (Outside Diameter). Use that measurement to determine which size fitting and hose is required for your repair.
Q: Do I have to replace the complete A/C hose assembly or can it be repaired?
A: No, you don’t have to replace the complete assembly. It’s typical that many hose sections leak at the hose crimp. That small hose section could be part of a long A/C hose assembly that’s costly to purchase, and does not need replacement. You can repair just the section of hose by cutting the ferrule and using a simple unique hose repair system that lets you replace the ferrule and hose section only. That way, you don’t have to replace the complete A/C hose assembly. You just replace the section of A/C hose that’s leaking. Repair kits are available on line.
Q: Can I repair the rear A/C hoses or lines on a vehicle with rear A/C?
A: Yes, you can usually repair the rear A/C lines that run under the vehicle for the rear evaporator. Typically, these hoses or lines are metal because they are exposed to all the harsh road and weather conditions as they run the entire length of the vehicle on underneath. In most cases, the entire line does not have to be replaced. (Complete line replacements are only available from the dealer). The rear A/C lines usually rust or corrode where there are clamps holding them or in areas where they have been exdposed.
To repair the lines, you first must be able to determine the actual size of the tube. With that, you can use the rear A/C line repair kits to fix just the section that’s leaking. Just cut away the corroded section and install the repair kit.Q: The A/C clutch will not engage. What could the problem be?
A: There are several different reasons why the A/C compressor clutch does not engage when you turn the A/C system on. Typically, the most common problems are:
1- Low refrigerant prevents the cycling switch from engaging the compressor. That’s because it’s acting as a safety for the compressor. This can be tested by jumping the switch. Also check system pressures. Low refrigerant pressures would indicate the charge is low and the system will have to be leak tested and recharged to fix the problem.
2- Clutch coils can also fail. The coil is what creates the magnetic field to ‘pull’ the clutch hub into the pulley, engaging the clutch. The coil can be tested using an Ohm meter to assure continuity.
3- Air Gap; That’s the distance between the front hub and the pulley. Typically, it should be about .025″ or about the thickness of a business card. When the air gap is too wide, the magnetic field is not strong enough to pull the hub in. The clutch air gap can be adjusted (usually on the vehicle).
4- Not enough voltage; the clutch requires a full 12 volts in order to create the required magnetic field. When contacts and connections are corroded, there may be a drop in voltage. Check voltage at the clutch to assure proper voltage is present.
Note that these are the most common reasons why the A/C compressor clutch does not engage. Other electrical problems (ie.: control head, relays, etc.) will require a wiring diagram for diagnosis.
Q: My A/C compressor clutch slips when the compressor engages. What is the problem?
A: Every A/C compressor clutch has a specific ‘air gap’. That is the distance between the clutch plate (or clutch hub) and the pulley. If the clutch is slipping when the compressor trys to engage, it is most likely that the air gap is too large. Typically the air gap will change over time. In most cases, the gap increases. When it increases too much, the clutch plate will start to slip when the compressor engages.
It should also be noted that there are other problems that could cause compressor clutch slipping; typically insufficient voltage or excess high pressures. Those possible causes require other equipment or pressure gauges to check.Q: My air conditioning system has a foul odor. Why is there an odor and what can I do to eliminate the odor?
A: The foul odor is a result of the basic design of the auto A/C system. The system is technically known as a ‘series re-heat system’. That’s because all the air entering into the vehicle passes over the evaporator regardless of whether you’re calling for cooling, heat or some blend of hot and cold air. Therefore, the air side (or inlet side) of the evaporator faces all the pollutants and contaminants in the air. Because the evaporator is usually wet or moist with condensation, that dirt and debris tends to stick to the evaporator face. Those are perfect conditions for the start of bacteria, mold and mildew. To eliminate the problem, you have to apply something to treat the odor and help eliminate the odor causing bacteria and mold. A good A/C Evaporator Treatment is available at the COOL ZONE. Also understand why foul odors from your A/C system happen.
Tight size of A/C Fittings and Hose:
The size of A/C hose required is determined by the size of the fitting or tube section that is used. There are four fitting sizes that will provide almost 99% coverage for all the A/C hose repairs. The tube O.D.’s (Outside Diameters) are 3/8″, 1/2″, 5/8″ and 3/4″. They are commonly converted to ‘number’ sizes as shown in the fitting size chart below.
Before you start, it’s important to understand where to take the measurement. In order to determine the proper fitting and hose size required for an A/C hose repair, you must take a measurement of the OUTSIDE DIAMETER (O.D.) of the tube section as close to the section of A/C hose as possible. You don’t have to discharge the A/C system to do this measurement, but you will have to recover the charge before attempting to remove the hose section and completing the repair.Measuring the tube or fitting size:
Simply measure the tube section of fitting size by taking a measurement of the tube O.D. (outside diameter) as close to the section of A/C hose as possible. Then refer to the chart below to understand what size of A/C hose or fitting is required to complete the repair.
A/C Hose and Fitting Chart:
You can quickly find out what size A/C hose or fitting is required from the chart below
TUBE or HOSE O.D. = Outside Diameter
TUBE or HOSE I.D. = Inside DiameterTube O.D. Nominal Size A/C hose I.D. A/C hose O.D.
3/8″ #6 5/16″ (.312″) 3/4″ (.750″)
1/2″ #8 13/32″ (.406″) 29/32″ (.906″)
5/8″ #10 1/2″ (.500″) 1″ (1.000″)
3/4″ #12 5/8″ (.635″) 1-3/32″ (1.09375″)
Note about the A/C hose sizes listed in the chart:
The above chart provides A/C hose I.D. and O.D. of standard barrier refrigerant hoses. In some applications, the original manufacturer may use ‘Reduced Diameter’ barrier hose. Reduced Diameter hose is the same INSIDE DIAMETER as standard barrier hose, but the OUTSIDE DIAMETER is reduced. It allows for tighter bends under the hood. However reduced diameter A/C hose can be replaced with standard barrier hose without any effect on fit or performance of the A/C system.
It’s also important to remember…:
If you’re replacing or repairing an A/C hose, you will require new o-rings or gaskets when reinstalling the hose. The actual o-ring sizes may not be the same as the fitting sizes that you’re replacing. That means that the hose assembly that you’re working on could be part of a long assembly that includes different sizes of fittings. Be sure you have all the right o-rings and gaskets to complete the job with leak free joints!
You will also have to recharge the A/C system when you’re finished.
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