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What is the function of the refrigeration pressure switch on the a/c system?

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There are two pressure switches. The one on the line going to the front of the car is to prevent too much pressure. The one on the line running towards your firewall is to shut off the compressor if the pressure is too low.

Posted on Dec 31, 2013

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The aircon system is fully gased yet the compresser wont engage, are there pressure switches in the system


Yes , two , a low pressure an a high pressure cut off switch . If either of these were bad there would be a DTC - diagnostic trouble code stored in the PCM - engine computer . Does your Captive have manual or automatic heating an A/C ?
Pressure transducer switching incorporates the functions of the high-pressure and the low-pressure cutout switches along with the fan cycling switch. The pressure transducer is located in the high-side liquid refrigerant line behind the right strut tower, between the right strut tower and the front of dash. The output from this pressure transducer goes to the electronic control module (ECM), which controls the compressor function based on the pressure signal.
HVAC Compressor Clutch Does Not Engage

1

Did you perform the Diagnostic System Check - Vehicle?
Go to Step 2
Go to Diagnostic System Check - Vehicle

2

  1. Start the engine.
  2. Turn the blower switch to any position except OFF.
  3. Press the A/C switch to the ON position.
Does the A/C compressor clutch engage?
Go to Testing for Intermittent Conditions and Poor Connections
Go to Step 3

3

  1. Connect a scan tool.
  2. Use the scan tool to command the A/C compressor clutch relay ON. When the relay is energized the cooling fan will also run at low speed.
Does the A/C compressor clutch engage?
Go to Step 8
Go to Step 4

Dec 04, 2015 | Chevrolet Captiva Cars & Trucks

1 Answer

Just replaced ac compressor and still not working. replaced a relay also. What would keep itfrom coming on?


Could have a faulty low pressure switch.
The low pressure switch is located on the air conditioning line in the right rear of the engine compartment near the firewall.

The low-pressure switch in your air conditioning system is used to interrupt power to the compressor when the low side pressure drops below 25 psi. This prevents freeze-up of the system and possible damage to the compressor. When the switch is faulty, the symptoms of freeze-up, or no compressor function, will be present. Replacement is straightforward, but requires the removal of refrigerant from the system.

Jul 03, 2015 | 2003 Kia Sorento

1 Answer

2007 ford KA blowing hot air


see this causes and fix it. God bless you
Compressor Checks
checkmark.gif Start with the compressor. Does it engage when you turn on the A/C?
If so, the compressor is working and the A/C system probably contains enough refrigerant to make cold air, so the problem is inside the HVAC unit. Replace the motor that controls the blend air door (this is a difficult job and best left to a professional since it involves tearing apart the HVAC unit -- about an 8 to 10 hour job!).
If the compressor does not engage when you turn on the A/C, see if it will run by jumping the compressor clutch wire directly to the battery (use a fused jumper wire). If the compressor works when you jump it, and the A/C blows cold air, the system contains refrigerant and the fault is likely a bad A/C compressor clutch relay or a bad clutch cycling switch or pressure switch.
If the compressor does not engage when you jump it, the problem is a bad compressor clutch.
If the clutch engages but the compressor does not turn (the belt will start to slip and squeal), the compressor is locked up and you need a new compressor.
If the compressor clutch engages and turns the compressor, but the A/C still does not blow cold air, the system is probably low on refrigerant and needs to be recharged.
Refrigerant Checks
checkmark.gif Connect an A/C pressure gauge to the HIGH SIDE service port (located in the high pressure hose that runs between the compressor and the condenser in the front of the engine compartment). The gauge will tell you if there is any pressure in the system. Simply depressing the service fitting valve with a small screwdriver to see if any refrigerant squirts out is NOT an accurate check because it tell you how much pressure is in the system. It may still have some pressure but not enough to trip the low pressure safety switch so the compressor will engage.
If your A/C system is low or out of refrigerant, check for leaks, then have the A/C system vacuum purged to remove air. After the air is out, it can be recharged with the specified amount of refrigerant. It is important to get any air out as this will reduce cooling efficiency and may make the compressor noisy.
A/C System Functional Checks
checkmark.gif If the refrigeration circuit seems to be working (refrigerant in the system, compressor running and building pressure), but there is still no cooling, the problem might be an obstruction in the orifice tube (located in the high pressure hose between the condenser in the front of the radiator, and the evaporator located in the passenger compartment). A blockage here will prevent the refrigerant from entering the evaporator or recirculating through the refrigeration circuit.
If the orifice tube is plugged, the high side pressure reading will be lower than normal, and the low side reading will also be lower than normal because no refrigerant is circulating through the system.
checkmark.gif If the refrigeration circuit seems to be functioning normally (compressor running, frost or condensation on the high pressure line from the condenser to the evaporator), but no cool air is blowing out of the ducts inside the car (and the blower is working), the fault is likely a BLEND AIR door that is stuck in the HEAT position, or possibly a badly clogged cabin air filter that is restricting airflow. Another possibility would be a fault in the automatic climate control system such as a ad interior temperature sensor or control module.

Sep 28, 2012 | 2007 Ford Ka 1.3

1 Answer

A/C compressor is not engaging


You need a technician. The system could be out of refrigerent, and this causes the low pressure switch to open thereby prohibiting the compressor clutch from functioning. The electromagnet in the clutch could have failed or it could be a switch or fuse problem. My guess is the low pressure switch though.

Jul 02, 2012 | Cars & Trucks

1 Answer

1997 jetta ac works for one minute then warm air blows


check the refrigerant level. The compressor is running until the low pressure or high pressure switch switch cuts it off.

Running the unit without enough refrigerant will damage the compressor because the lubricating oil is dissolved in the refrigerant. This is the reason for the low pressure switch cut off--to protect the compressor from damage.

If pressure gets too high, the compressor seals will blow. Thus the reason for the high pressure switch. Too much refrigerant or too much air in the system (due to a leak) will cause high pressures.

If refrigerant level appears to be correct, then suspect trapped air from a leak causing a high pressure cut-off. If refrigerant is low, suspect a leak causing a low pressure cut-off.

Mar 02, 2011 | Volkswagen Jetta Cars & Trucks

1 Answer

My A/C stopped blowing cold air How can I diagnose problem


No Blower or just lost A/C function. Just A/C, Look for refrigerant leaks,electronic leak check leaks, scan for a/c related data,put gauges on system and pressure check. All good you got pressure switches and more. Forgot to watch for compressor clutch engagement assuming you have system pressure. That's a start ,will keep you busy for a couple hours. Let us know how you make out.

Sep 29, 2009 | 2000 Oldsmobile Silhouette

1 Answer

Have a 2003 stratus with intermittent A/C works great when on, where is the pressure sensor located?, that may be problem


On this Chrysler product they have an A/C Transducer located on the high pressure hose. The switch has three wires. They also have a thermo sensor located at the evaporator case behind the glove compartment. These two things are the only ones thatA jump in the system is only removing protection the system has. So it will damage your compressor or hoses. Find the compressor follow the high hose to the high pressure switch (transducer) it has three wires. Check under the dash by the glove box and you will see a round platick lid on the case with two wires that is your thermostat (thermo sensor).
control the compressor.

The A/C clutch is controlled by the A/C cycling switch (19E561) and the A/C pressure cut-off switch, which are connected in series. The A/C cycling switch is mounted on the suction accumulator/drier (19C836), and the A/C pressure cut-off switch is mounted in the discharge line at the A/C condenser.

The A/C cycling switch closes when the pressure on the low side of the system reaches approximately 276-324 kPa (40-47 psi). The A/C cycling switch opens when the pressure drops to approximately 163-175 kPa (23.5-25.5 psi), disengaging the A/C clutch. In ambient temperatures below -1° C (30° F), the A/C cycling switch will not allow compressor operation because of low system pressures.

The A/C pressure cut-off switch is used to interrupt A/C clutch operation in the event of high system discharge pressures. The A/C pressure cut-off switch is a single-function switch that controls A/C clutch engagement. When compressor head pressures rise to approximately 2896 kPa (420 psi), the contacts open, disengaging the A/C clutch. When the pressures drop to approximately 1724 kPa (250 psi), the contacts close to allow A/C clutch operation.

This problem can be caused by low refrigerant charge. Check with a manifold gauge set and temperature pressure chart.
The cycling switch is replaceable and there is a Schrader valve on the accumulator port so you do not lose your system charge when replacing. It screws on/off. It is available at any auto parts store. It protects the compressor from low pressure which can be caused by a loss of refrigerant and subsequent lack of lubrication and prevents evaporator freeze up. Replace the switch. It is about $10. The high presure switch is about $25.

Aug 26, 2009 | 2003 Dodge Stratus

2 Answers

''does a new radiator need refrigerant added to it''


You need to replace the condensor, then take it to a shop to have the a/c system evacuated and recharged to purge moisture because the system was opened. That will cost around $150. You do not need to replace the receiver/dryer/suction accumulator even though they will tell you that you do.
go to car-part.com to find prices of condensor from salvage yards. Page with asterisk on it is the lowest priced part.

--------------------------------------
The Refrigerant Cycle
During stabilized conditions (air conditioning system shutdown), the refrigerant is in a vaporized state and pressures are equal throughout the system. When the A/C compressor (19703) is in operation it increases pressure on the refrigerant vapor, raising its temperature. The high-pressure and high-temperature vapor is then released into the top of the A/C condenser core (19712).
The A/C condenser core, being close to ambient temperature, causes the refrigerant vapor to condense into a liquid when heat is removed from the refrigerant by ambient air passing over the fins and tubing. The now liquid refrigerant, still at high pressure, exits from the bottom of the A/C condenser core and enters the inlet side of the A/C evaporator core orifice (19D990).
The A/C evaporator core orifice is the restriction in the refrigerant system that creates the high pressure buildup in the A/C evaporator core (19860) and separates the high and low pressure sides of the A/C system. As the liquid refrigerant leaves this restriction, its pressure and boiling point are reduced.
The liquid refrigerant is now at its lowest pressure and temperature. As it passes through the A/C evaporator core, it absorbs heat from the passenger compartment airflow passing over the plate/fin sections of the A/C evaporator core. This addition of heat causes the refrigerant to boil (convert to gas). The now cooler passenger compartment air can no longer support the same humidity level of the warmer air and this excess moisture condenses on the exterior of the evaporator coils and fins and drains outside the vehicle.
The suction accumulator/drier (19C836) is designed to remove moisture from the refrigerant and to prevent any liquid refrigerant that may not have been vaporized in the A/C evaporator core from reaching the A/C compressor. The A/C compressor is designed to pump refrigerant vapor only, as liquid refrigerant will not compress and can damage the A/C compressor.
The refrigerant cycle is now repeated with the A/C compressor again increasing the pressure and temperature of the refrigerant.
The A/C cycling switch (19E561) interrupts compressor operation before the external temperature of the A/C evaporator core gets low enough to cause the condensed water vapor (excess humidity) to turn to ice. It does this by monitoring low side line pressure. It is known that a refrigerant pressure of approximately 210 kPa (30 psi) will yield an operating temperature of 0°C (32°F). The A/C cycling switch controls system operation in an effort to maintain this temperature.
The high side line pressure is also monitored so that A/C compressor operation can be interrupted if system pressure becomes too high.
The A/C compressor pressure relief valve (19D644) will open and vent refrigerant to relieve unusually high system pressure.
Clutch Cycling Orifice Tube Type Refrigerant System 75cc8eb.gif
Item Part Number Description 1 19E762 A/C charge valve port (low side) 2 19E561 A/C cycling switch 3 19C836 Suction accumulator/drier 4 19703 A/C compressor 5 19D644 A/C compressor pressure relief valve 6 19D594 A/C pressure cut-off switch 7 19E762 A/C charge valve port (high side) 8 19712 A/C condenser core 9 19D990 A/C evaporator core orifice 10 19860 A/C evaporator core 11 — Low pressure vapor 12 — High pressure vapor 13 — Low pressure liquid 14 — High pressure liquid

  1. Connect the R-134a A/C Refrigerant Center to the low- and high-pressure service gauge port valves.
  2. Evacuate the system until the low-pressure gauge reads at least 99.4 kPa (29.5 in-Hg) (vacuum) and as close as 101.1 kPa (30 in-Hg) as possible. Continue to operate the vacuum pump for a minimum of 45 minutes.
  3. Turn off the evacuation pump. Observe the low-pressure gauge for five minutes to make sure that the system vacuum is held. If vacuum is not held for five minutes, leak-test the system, service the leaks, and evacuate the system again.
  4. Correctly oil match the system to verify that the correct amount of refrigerant oil is present in the system. For additional information, refer to Refrigerant Oil Adding in this section.
  5. Charge the system with the specified weight of refrigerant and refrigerant oil.
  6. When no more refrigerant is being drawn into the system, start the engine and select MAX A/C operation. Set the blower motor speed to maximum and allow the remaining refrigerant to be drawn into the system. Continue to add refrigerant into the system until the specified weight of R-134a has been added. Close the charging cylinder valve and allow the system to pull any remaining refrigerant from the hose. When the suction pressure drops to approximately 207 kPa (30 psi), close the charging hose valve.

May 14, 2009 | 1995 Nissan Maxima

2 Answers

A/c blows out hot air, and when i hooked up a can of a/c charger the gauge on the can was in the red, saying i need professional help any ideas as to what the problem is? im hoping its not the compressor,...


Jonathon,
I am amazed at some of the answers you have received so far. Let's get a few things straight, first, if your car is a 2006 model sold in the USA, you have an R134a system (mandated by federal law since 1996), so the answers that included mixing refrigerants are of no value. Second, if your system was working last year and you have not added any refrigerant since then, there is no way for your system to be overcharged. Assuming you are speaking of pressure in PSI and temp in degrees Fahrenheit, you are describing the static pressure in most R134a systems. By static I mean the pressure with the compressor not running. At 100 PSI of static pressure, your system is probably undercharged. You may have turned on your AC system inside, however you did not state that you can see the AC compressor clutch actually engaging and turning the compressor. Modern AC systems have low pressure cut out switches that will prevent the system from operating under low pressure conditions to protect the compressor. If you can observe the compressor clutch, watch to see if it is engaging and turning the compressor. If not, you have to make a small jumper (I use a small paper clip) to jump the low pressure switch plug (usually located on the compressor or accumulator) and spin the compressor. If that woks take another reading with your pressure gauge and I think you will find a reading somewhere below 30 PSI. You can then charge your system until you obtain a proper charge. Be sure to re-install the low pressure switch plug when finished.
If your AC compressor clutch is engaging and turning the compressor and your low side pressure is 100-150 PSI, then you do actually have a problem that will require professional assistance. Your compressor is either not functioning properly or there is some obstruction in your system that is preventing the refrigerant from circulating properly. Good luck.

Apr 26, 2009 | 2006 Suzuki Forenza

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