So, if you really want to diagnose and fix your AC system yourself. If the compressor is running (center portion of the pulley is turning), the compressor is spinning but not pumping. not acceptable, change to a control based on ambient air temperature,
charts of the compressor for the maximum suction pressure. Flooded head pressure control: Bypass port wedged
Moisture in the system causing the expansion valve
conditions. This is called superheat and in an orifice tube system, the superheated refrigerant is what causes evaporator icing. Because, on an R-134a AC system, 27-psi. Consider all the factors, including ambient temperature, condenser airflow, engine rpm and humidity, which all affect the manifold gauge readings. Refrigerant shortage or lacking a winter charge. Damaged valves or rods in the compressor. If there has been an oil loss for any reason, repair the cause of oil loss and refill according to the Refrigerant Oil Capacities chart in the Service Manual for the vehicle being serviced. 
Blower set to HIGH speed 3. External equalizer line plugged or capped. One of the benefits of using electronic leak detection is being able to detect leaks at the time of A/C service. This can be caused by a stuck air temperature door, faulty air temp/blend door actuator or, in older systems, a stuck open heater control valve thats running hot engine coolant into the heater core even though the heat is set to cold. poor air distribution.
This may be a situation where the AC is working fine but the heat is on, diminishing the effects of the AC. Install pump Ambient Temperature in F Low side Pressure Gauge reading and High side Pressure Gauge reading 65F Ambient temperature: Low side pressure 25-35 psi High side pressure 135-155 psi 70F Ambient temperature: Low side pressure 35-40 psi High side pressure 145-160 psi 75F Ambient temperature: Low side pressure 35-45 psi High side pressure 150-170 psi 80F Ambient temperature: Low side pressure 40-50 psi High side pressure 175-210 psi 85F Ambient temperature: Low side pressure 45-55 psi High side pressure 225-250 psi 90F Ambient temperature: Low side pressure 45-55 psi High side pressure 250-270 psi 95F Ambient temperature: Low side pressure 50.55 psi High side pressure 275.300 psi 100F Low side pressure 50-55 psi High side pressure 315-325 psi 105F Ambient temperature: Low side pressure 50-55 psi High side pressure 330-335 psi 110F Ambient temperature: Low side pressure 50.55 psi High side pressure 340.345 psi. Flood back due to poor distribution of refrigerant If the gauges dont read the same during a static pressure test, it means: 1) You havent waited long enough for the pressures to equalize, or. So the refrigerant picks up too much heat. Air Conditioning (A/C) pressure diagnosis can also help pinpoint the concern with a malfunctioning system. Be careful; high-pressure refrigerant lines may become very hot! If your pressure gauge readings are not within factory specifications, there is a problem in the system. If the restriction is located before the high-side service port, your readings will be lower than normal. Rerun the load the refrigerated or air condition space etc. The system is overcharged, theres a lack of airflow across the condenser (clogged fins, radiator/condenser fans not working or not working at the proper speed), or you have air and moisture in the system. Voltage out of balance on 3 phase systems. Oversized evaporator or undersized compressor. Read the pressure gauges and compare them to factory specifications. They are just a guide to aid you in your diagnosis. This will leave refrigerant in the low side Is it a cycling clutch orifice tube system or an expansion valves system? which creates the possibility of flooding on start up. Compressor malfunctioning, possibly leaking valve. You need to use these readings, other symptoms, the Service Manual and your knowledge of system operation to find the trouble with the system. Restriction in the low side of the system. This may be accomplished with the vehicle service valve or a refrigerant container. They transfer heat from one place to another.
Flooded head pressure control: Receiver too small Static pressure is the pressure with the system at rest (compressor off for at least 30-mins).
External equalizer lines tapped at a common point Maintenance Advantage program.
If you dont know the difference, you cant diagnose by pressures. open due to a foreign material lodged in it, or the port is worn. Electronic leak detectors must meet or exceed SAE J1627 to operate properly on R-134a. WARNING: Ambient temp is the temperature at the vehicle under the hood, NOT THE WEATHER SERVICE. If the terminal has threaded studs and nuts, a Find the leak and fix before refilling. The use of a Crankcase If not, refrigerant pressure can be supplied from a charging station although it is not necessary to completely charge a system for leak testing. It takes a while to equalize, thats why you must wait 30-mins to check static pressure. Faulty low pressure control, temperature control, Smooth coolant flow through the heater core is critical for heat output. have a bleed resistor?
NOTE: Low airflow across the evaporator, caused by a plugged cabin air filter, can mimic the symptoms of a low refrigerant charge. the compressors ability to start and run. check the pressure dome settings. with an ambient temperature above 33) the AC system will not engage the compressor and you will not get any cooling. The valve is usually located under the hood and is opened and closed by a vacuum motor or cable. This is common on walk in coolers and freezers when
By reading the gauges alone, you may be misled into making an inaccurate diagnosis. var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
Check the low ambient control. However, knowing what the gauges say can be troublesome for some technicians. In this manner, refrigerants change states as required by the system. youll need an AC manifold gauge set and hoses. Normal compressor cycling on a rack system. Too much oil will reduce the cooling capacity of the system. When properly charged, a full evaporator will spill some boiling refrigerant into the accumulator where it will continue to vaporize before entering the compressor. superheat at evaporator outlet. Incorrect air flow thru the condenser. Control voltage too high, causing premature trip
Liquid refrigerant backed up in the receiver. down controls and a crankcase heater. Expansion valve or metering device too large. Compressor manufacturers are very concerned about the addition of lubricants other than those specified on the vehicles label. 
If the cabin air temp is controlled by an air temp/blend door, check actuator operation to see if it moves as you change the temperature setting. Check the arrow
Turn on the leak detector. Probably in the evaporator. If the suction line is cold with the system operating, there is usually enough refrigerant in the system to perform the leak test. 5. A compressor overheating will break down the wiring connections. However, adding more than specified to the A/C system will not make the leaks more obvious. Close the doors. hot gas bypass valve or capacity control valve.
Insufficient refrigerant charge, usually accompanied
If the air is not removed from the system, the system will have performance problems. 3. Flooded head pressure control: Field adjustable Fan cycle control: This is normal if this type Excessive liquid refrigerant returning to the compressor For more information on normal AC pressures, see the charts below. NOTE: Refer to the HA section in the ESM for the applicable vehicle for pressure readings at various ambient temperatures and the setting the AC should be on when diagnosing with pressure gauge readings. Overcharging actually REDUCES cooling and undercharging can damage the compressor (refrigerant carries the lubricating oil so low refrigerant = oil starvation for the compressor). in the compressor. is restricted. Place a temperature gauge in one of the air outlets in the passenger compartment.
Fans and blowers move fresh or recirculated air across the evaporator fins and heater core to provide heated air for the climate control system. Generally speaking, you want around 27-psi on the low side and 200 on the high side. Water cooled: Restricted water flow, water too air conditioning troubleshooting chart basic repair guide autozone fig problems 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; You need to verify what is wrong before replacing any parts. Using a Go/No-Go refrigerant detector for both service situations can only identify system contamination. Incorrect starting relay. with the compressor manufacturer. A large puddle is an indication of evaporator ice that has melted and drained onto the ground. Check the performance Drier/liquid tank). You may be required to add up to a pound of refrigerant in order to locate the leak. Cool Automotive Products and Tool Recommendations, Read AUTO REPAIR ARTICLES sorted by topic, My opinion of the FortNine Youtube Fuel Stabilizer Test, My opinion on Project Farms Fuel Stabilizer Testing Video, Custom Wordpress Website created by Wizzy Wig Web Design, Minneapolis MN. Determine if the vehicle has a heater control valve. Refrigerants are the vital working fluids in refrigeration systems. Excessive load on the evaporator above the design The ice blocks airflow and the low pressure triggers the low-pressure switch. System contamination, probably moisture or rarely, This will enhance the luminescence of the dye, which will make the smaller leaks more apparent. Expansion valve power element has failed or lost When you suspect a problem, try using the hand-feel temperature test on the lines and hoses to find restrictions in the refrigerant system. up. Oil pressure control defective or improperly wired. The ambient temperature surrounding the condenser or capped. A tool that can identify the contents of an A/C system is essential in some diagnostic situations. Compressor oversized and the evaporator is undersized. To find a leak with an electronic leak detector: 1. The compressor will shut off once the low pressure triggers the low-pressure switch. chart air cfm pressure ac airflow blower flow residential ton evaporator coil tool performing setup figure system through Air flow is restricted thru the condenser. Ruptured suction line to the liquid line heat exchanger. Has someone Liquid refrigerant feeding through the oil separator. caused by poor air distribution. calculations. Get the BEST auto repair information Alldatadiy.com and Eautorepair.net are professional-grade shop manualsperiod. Internally equalized expansion valve used on a Look, I know you want to figure out your AC problem yourself without buying any tools, but you can really screw up your cars AC if you overcharge or undercharge the system.
A higher percentage mixture (more than 50 percent) will decrease heater performance. 2. At 200-psi. Excessive suction pressure beyond the limits of You cant accurately diagnose your cars AC by using just the low-pressure gauge on a recharge kit because youre only seeing pressure on the suction or low side of the entire system. Does the start capacitor out. However, in a partially filled evaporator, the vapor then absorbs heat. Always refer to the manufacturers instructions for proper use of the refrigerant analyzer. line without a liquid injection valve.
125 PSI / 30 PSI = The system is either not charged enough or you have too much oil in the compressor. Also, a faulty evaporator temp sensor can prevent the system from shutting down once the evaporator has iced over.
It is very important to have the correct amount of oil in the A/C system. If this is a problem, use low-pressure compressed air or a fan to blow any released refrigerant from the engine compartment before leak testing. Obviously the main issue that people deal with when they have a broken A/C system is that the air coming out the vents is not cold enough. 4. We have reviewed over 1,000,000 fitments to guarantee an exact fit for your vehicle.
225 PSI / 80 PSI = It is likely that the expansion valve is opened too wide (not the case if your A/C system has an orifice tube) Also, you could have too much refrigerant in the system. 4. Liquid line solenoid valve leaking during the off Once the evaporator ices over, you should notice a dramatic reduction in airflow from the vents. Pressure Regulator (CPR) or pressure limited TXV (MOP) may be required. That, in turn, causes the evaporator to freeze up which shuts off the AC. OR, continue driving the vehicle with the blower on HIGH while monitoring airflow from the vents.
If the gauge reading is normal when first turned on and stays normal for a few minutes, you get cold air and THEN low side goes low, thats a sign of moisture in the system.
250 PSI / 50 PSI = The system is overcharged and the condenser is not cooling. NOTE: Refrigerant oils (PAG lubricants) are available through the Nissan to an undersized liquid line or excessive vertical lift. With an ambient temperature of 70 F (21 C), an orifice tube system with a cycling switch should have approximately 150-250 psi (1034.2-1723.7 kPa) high-side pressure and 24-31 psi (165.5-213.7 kPa) low-side pressure. Superheat setting on expansion valve too high. ga.src = ('https:' == document.location.protocol ?
You could have a low-pressure reading on the high-side gauge and still have a restriction on the high-pressure side of the system. Check amp draw verses suction pressure verses condensing temperature of a Crankcase Pressure Regulator (CPR) or pressure limited TXV Measure ambient air temperature at the vehicle and under the hood WITH A THERMOMETER (do not use weather service temperatures). If your readings are outside the typical pressure/temperature range, see below. Thats an indication of a bad compressor. Lack of an oil separator on freezer systems.
Expansion valve defective or has the incorrect
Recovery equipment that has an automatic shutoff at a predetermined vacuum level will not reach that level if a leak exists. 
The expansion valve is stuck open so the system cant build pressure or the thermal bulb that measures evaporator temp isnt working properly and is causing the expansion valve to remain open. Available in the contiguous U.S. only. The pattern will repeat over and over. Although large leaks will show up quickly, small leaks may take several days to appear using this method. The leak detector may not operate effectively if any refrigerant has been released under the hood from gauge hook-up or charging. ceiling.
As you go over the system, using the black light to check for indications of trace dye, do not forget to check the evaporator condensate drain. Place a second temperature gauge at the condenser to measure ambient (outside) air temperature. To perform the leak test, the system must be under pressure. Let the system operate for 5 minutes. Re-circulating of condenser air.
Note that pressure gauge readings vary with ambient air temperature, humidity and system design. Expansion valve distributor or cap tube restricted. system where all the EPR valves are wide open. ac readings pressure side normal system youfixcars elevated higher than wrong
Defective compressor overload which will cause For example, a restricted orifice tube will cause the compressor to suck, but the restriction/clog in the orifice tube prevents the full flow of refrigerant, causing evaporator starvation. the compressor for the maximum suction pressure. power element charge. However, recycling equipment with a manually operated purge can allow high levels of air into the system usually due to technician error.
document.getElementById( "ak_js" ).setAttribute( "value", ( new Date() ).getTime() ); Enter your email to receive an instant discount. This also applies to trace dye; therefore, only use trace dye that meets or exceeds Nissan or Infiniti approval. Refrigerant analyzers are available that meet or exceed SAE J2912 and can identify gas samples taken directly from the refrigerant system or storage containers. The system pressure is high enough to enable compressor clutch engagement. material causing liquid flood back. Most electronic testers have a thumbwheel to adjust detection sensitivity. See the tester documentation for this procedure. NOTE: Trace dye is mixed with the PAG lubrication oil. low. Evacuate the system and recharge with the correct refrigerant charge and test again. High side normal to slightly low Causes: Low on refrigerant charge.
wax. The unit displays FAIL if R-134a gas has not been identified or if it is not at least 98 percent pure. Free, one year (or more), unlimited mileage warranty. Uninsulated receiver in a cold ambient acting as Thats not enough information to diagnose a problem. If the fluctuating pressure is horsepower and blade size, compared to the specifications of the
Expansion valve defective or held open by a foreign If the visual inspection fails to reveal the source of a refrigerant leak, test the system using either an electronic leak detector or a trace dye. After analysis is made and displayed, the analyzer purges the unit of the sampled refrigerant and is ready for the next sample. There are several PAG oils with special additive packages and different viscosities, which are used in current Nissan and Infiniti vehicles, depending on the type of compressor used. It is important to use the correct oil for the type of compressor being serviced. If the recovery unit has a properly operating automatic purge, usually it will vent the excess air. First, check the engines coolant level. Incorrect capacitor, capacitor voltage rating too freeze up when this occurs. You should also be aware that there are different types of electronic leak detectors. small.
Product, people, heat producing equipment in
In most cases, their diagrams are right from the factory manuals. any two circuits as they enter the header. Now that you are familiar with some diagnostic testing methods, it is time to evaluate some of the more common diagnostic scenarios you may encounter. })(); Oil trapping in the system. If the container pressure is not checked, air will transfer into the system. valve.
Or, if you can access the orifice tube, apply heat to the orifice tube as you watch system pressures. Thats just around the freezing point of water. Crankcase heater not installed or defective (migration). These charts give you pressure readings and possible causes to check to pinpoint the cause of the concern. What are my A/C pressure readings telling me about my A/C system. 
Worn bearings, cylinder walls and piston rings
control.
160 PSI / 10 PSI = It is possible that the evaporator is frosted, the low pressure piping is faulty, or the expansion valve might be clogged. For more troubleshooting tips using gauges, see this post. Dirty condenser causing high pressure cut out. Equipment with an automatic air purge usually keeps the air contamination level at less than 2 percent by weight, which is considered acceptable. Manual reset low or high pressure control lockout. Too little oil will damage the compressor. is inconsistent. NOTE: For more information regarding refrigerant contamination or disposal locations, contact the Environmental Protection Agency (EPA) hotline at 800-296-1996 or over the Internet at www.EPA.GOV/ozone. (function() {
Check the specifications Remember, these are the locations on the system where your gauges actually monitor the pressure. This not only enables the system to operate efficiently but also ensures proper lubrication of the compressor. An AC system leak allows moisture into the system. The use Fan cycle control: This is normal if this type So, if the ambient temperature is 80F, youll see high side pressures running between 176-psi and 200-psi. If the A/C system is not cooling the vehicle to factory specifications: check to see if the A/C compressor clutch is engaged and the A/C system is fully charged.
Any trace dye coming out of this location is a sure sign of an evaporator leak. although there is more than one expansion valve on the same system. However, Alldatadiy.com also includes disassembly instructions for interior trim panels and exterior items like headlights and tail lights. for summer application. That saves a lot of time because you dont have to refer back to the component locator or circuit locations.
running continuously.
NOTE: Always wear the protective eyeglasses that come with your black light equipment. In other words, the low refrigerant charge causes the refrigerant is in the system to sit too long in the evaporator. its charge. Here is a list of the pressure readings that are characteristic of an A/C compressor that is not blowing cold air into the cabin of your car: 250 PSI / 30 PSI = You have air somewhere in the system.
Keep in mind that AC pressures and center duct temperatures are directly related to ambient temps and relative humidity. Usually corresponds with high superheat at the
Evaporator pressure regulator( EPR) valve faulty. Before you make any determination regarding the pressure gauge readings, you need to consider the service port locations. In some cases, the fix can be as simple as replacing an actuator. For More Free Troubleshooting Information Please Visit Our Home Page. Then youll get cold air againuntil the evaporator ices up again. There should
External equalizer on the expansion valve plugged
cycles. Finally, always attach the trace dye identification sticker in the engine compartment close to the A/C decal. The tool may also be required for A/C service centers according to regulations in your area. There are also different types used in A/C service; therefore, it is very important that you use the correct type. Copyright 2022 Buy Auto Parts. No traps or insufficient traps in the suction riser. Water cooled: Water too cold or defective water Rubber hoses deteriorate over time and rubber particles clog the orifice tube screen. Once you attach your gauges and start your engine, keep RPMs steady at around 1,200 to 1,500 RPM. port wedged open due to a foreign material lodged in it. Covers everything; parts and shipping costs. Defective oil pump or the oil pump inlet screen For further information on this method of leak detection, refer to the instructions provided with the dye. warm, condenser tubes restricted or defective water regulating valve. Moisture in the system reacts with the refrigerant and oil to form acids and sludge that clog orifice tube screen Moisture in the system that freezes at the orifice tube and restricts refrigerant flow through the orifice. The recovery unit will continue to operate, drawing in air from the leak source and adding it to the storage tank. Restriction in the discharge line due to physical To locate the source of a large leak, listen for a hissing sound or spray some soapy water on components and look for bubbles. Excessive suction pressure beyond the limits of Then checking cooling. A leaking A/C system indicates the system refrigerant level is lower than specification. On the high side, R-134a pressures usually run 2.2 to 2.5 times the ambient temperature entering the condenser. Air can also be added during the refrigerant recovery process from system and service hose leaks. This is a common Flooded head pressure control: Pressure drop thru Rerun the load calculation. NOTE: High humidity and airflow velocity across the evaporator and condenser have a direct effect on pressure readings. voltage out of balance. High supply voltage, light compressor load. However, ambient humidity also affects how your cars AC works because high humidity changes how the heat transfers. the condenser exceeds 20 psi, forcing the bypass port to partially
Symptom: Low cooling Pressure readings: Low side is low.
2) The orifice tube, expansion valve, compressor reed valves or stuck or theres a severe restriction somewhere in the system thats preventing the pressure from equalizing.
Water cooled: Water is inadequate and the temperature improperly on the system. troubleshooting ac guide reading ask questions trutechtools lonely downloadable resources
An A/C System that is working properly should have 150 PSI on the high side and 30 PSI on the low side. For more information on Interpreting AC Pressure Readings, check out our How To page on the subject. the condensing unit is mounted on the box and closed off by a drop For example, if the high-side service port is located on the liquid tank and the hose between the condenser and the liquid tank is restricted, your gauge readings will be lower than you may expect.
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