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OK, short intro to a long post! My son bought a 2011 Hyundai Sonata. We noticed on test drive that the AC was warm at idle, we asked the seller, he disclaimed any AC problems and said it was normal. During the test drive, it cooled of at speed. A day after purchasing it that the AC would get really hot at Idle, work better at speeds...sometimes…and then it finally stopped cooling altogether, day 3 of ownership!!! Buyer beware~!

After hours of searching forums and youtube videos, NOBODY had enough information to solve this problem. So after researching this to death, I just went to work troubleshooting it and solved it myself! I may do a video explanation also on my Youtube channel “Howtoheaven,” in the future. Since I could not find any real help. I have decided to share my troubleshooting tips to help others that may have 2011 Hyundai Sonata AC problems. This is long, but to troubleshoot properly it is a must that you understand the components and general workings of this system. I cannot explain, on this forum, how to trouble shoot all problems, but this should help with the most common ones.

First, the 2011 Sonata was the first year to get the Variable compression AC compressor. This was a Toyota invention that I believe dates back to 1997, and is licensed to Hyundai, VW and I'm sure other manufacturers. It is a digital system!! So do NOT try and run 12v power line to the compressor!!! There is no Clutch Coil!

This is going to be long but hopefully comprehensive! I did not have access to schematics and just logically figured out the system by observation. I was once an HVAC tech.

Overview of the Components:

The main components are the AC controller (basically the switch panel with the fan/ temperature and mode switches mounted to it), the AC Compressor (which includes the AC controller valve, attached to it), the Transducer switch (aka pressure switch), which is connected to the high pressure line (the small line), the AC Expansion valve (it is attached to the fire wall, has a black plastic snap on cover, is aluminum, rectangular and has both the thick AC line {suction side/cold line}, and the thin AC line (pressure side/hot line) attached to it), the evaporator coil (mounted inside the dash and un-viewable), the evaporator temperature sensor (mounted at the front most, passenger side of the console, under a removable plastic snap on cover, and it plugs into the evaporator housing and is a twist and pull type sensor), and finally, the condenser (a radiator like aluminum unit mounted in front of the black Car Radiator, you can see the AC lines connected to it.).

In order to trouble shoot the system, you need to understand its components, so here goes!

What makes this system so hard to troubleshoot is that it is NOT an Analog AC System, it is a Digital System! The Compressor, compresses the Freon, variably. It does not have an AC clutch! And the compressor is always on! The pulley on the AC compressor looks like a standard clutch, but it is ONLY a pulley!!

The compressor has what is called a Swash Plate inside it. The Swash Plate is like a variable angled spinning disc, it changes the stroke of the compressor pistons, by changing the angle of the swash plate, thus, varying the compression and the amount of freon it pumps. This system was introduced to squeeze every MPG out of the car. A standard compressor is either ON or Off, the variable compressor is low and behold, VARIABLE, thus saving fuel…and wear and tear on the engine! It turns on and off based on a number of variables such as engine speed, temperature etc.

The brains of this system is the AC control board, which is mounted in the center dash AC controls. This board actually is where the fan, temperature, and mode switch are soldered to. My Sonata had manual AC controls, but I would bet that the dual climate control panel also has a logic circuit board mounted to it, and serves the same purpose of controlling the AC compressor, fan and mode switches, but is more adjustable for temperature.

The AC compressor has an AC controller valve that is replaceable and should measure between 10-14 ohms resistance. It has two wires coming off it, and is a pulsing power source (PWM pulse width modulated). A standard compressor only has one, +12v wire running to the coil. This AC controller valve is replaceable, but you must drain the Freon first, as the switch and compressor are under pressure. The AC controller valve is held in place by a single Snap Ring, that you remove, and then you just wiggle the AC controller valve, side to side and twist it to remove it. If you replace it, use some PAG AC oil to lubricate the o-ring before sliding the new one in.

So here is a super simplified explanation of how an AC system works! The AC system is basically a heat exchanger. In order to do this it needs a vehicle to move heat from one place to another. That vehicle is Freon. The brains of the system is the AC controller, not the one mounted to the compressor, but the control switch panel in the car. When you call for AC by turning the AC on and Turning the temperature to cool, the controller sends a signal to the AC compressor controller valve that then varies the angle of the swash plate according to how much cooling the AC controller and switches are asking for. The compressor pumps the Freon liquid to the AC expansion valve, which allows the liquid Freon to expand, changing it to a gas and super cooling it. The cooled gas then goes into the Evaporator radiator in the car and a fan blows the vehicle’s warm interior air over the super cooled coil. The air blowing over the evaporator exchanges the heat from the car and the super cooled temperature from the Freon gas. The cooled air is blown into the car and the heated Freon then flows out to the condenser, in front of the radiator, where the ambient air hitting the Condenser cools the heated Freon. The AC compressor then takes the gas and compresses it to a liquid again and the cycle continues again.

Ok so here is the troubleshooting!!

1) You need to determine if the AC compressor is running. You CANNOT do this by looking at the AC Compressor pulley and listening for a click! The easiest way is to connect AC gauges to both the high pressure, thin metal line on the car, remove the cap with the “H” printed on it, use the red hose on your gauges, and then connect your low pressure side, the thicker metal line, remove the cap with the “L” printed on it and use the green hose from your gauges. IF you have 134a gauges then you will find that the connectors are different sizes, so the quick connector only connects to the appropriate side. Turn on the AC at the control panel and watch the gauges, if the compressor turns on, you will immediately see both gauge needles move. Note, when the AC is turned off, the pressure in the system will equalize and the pressure should read about the same as ambient temperature on both the high and low gauge, i.e. if it is 85 degrees outside, both the low and high side pressures should read approximately 85 psi. If your low pressure gauge is nowhere near the ambient or room temperature (as explained above)…then it’s low and you need Freon and have a leak somewhere that needs to be fixed. When you turn the AC on, the low side pressure should drop to somewhere around 35-45 psi. The high side will go up over 150 psi. If you don’t have
2) If the compressor does not come on, meaning the pressures do not change at all or move a little and then stop moving (remember this system pumps pressure all the time, even when the AC is off….although it may only be a little), then you need to see if the compressor is getting power. To do this, depress the connector located on the compressor and pull the plug off….do this when the engine is off! The signal to the compressor is a digital Pulse width modulated voltage. Basically, a voltage pulse is sent to the compressor and more cooling required the more the pulsed voltage is ON. If your tool arsenal is large, you may have an oscilloscope that you can connect to the connector to see the pulses. If you only have a Volt meter (DVOM, like the free ones Harbor Freight gives away), just check for voltage. With the ignition on, but engine off (KOEO), you should get at least 10 volts. It won’t read 12 volts because remember, this is a pulse modulated system so your DVOM or meter is averaging the pulses, you should get approx. 10 volts. If you get 10 volts, then your AC Compressor control valve is probably bad and you can either drain your Freon and replace it alone, or you can drain your Freon and replace the entire AC compressor unit, that comes with a new valve, pull a vacuum, recharge your AC and your problems should be solved.
3) If you only have 4 volts, then you need to find out why the AC Controller is Not sending the right PWM signal to the compressor.
4) The first check should be you transducer switch also known as the Freon pressure switch/multi switch. It is located on the front passenger side wheel well on the high pressure/ small line close to the radiator. It has a plug on it that you push the retainer and remove. Do this with the power off. You must also drain the Freon to compare it to the new unmounted switch! If you don’t drain the Freon, then the pressure will give you a different reading than the new switch….you must compare apples to apples! Set your meter to read resistance and take readings from the 3 pins on the switch, and compare the readings to a new switch. If you don’t use/install the new switch, you should be able to return it. Make sure you check the readings between the first and last pin, the first and second pin and the second and third pin. Then compare it to the new switch. It should be easy to tell if the switch is bad as the reading will be way off. Pay attention to the meter, there is a huge difference between M ohms and K ohms (I won’t go into it but it’s huge). If this switch is bad, your compressor won’t get the right signal to turn on! If you replace it, remember to use some PAG AC oil to lubricate the o-ring before screwing the new one on and also use 2 wrenches, one on the line and one on the transducer…I actually used a 24mm socket on the transducer
5) If the Transducer switch is good, then check you Thermostatic Temperature switch, located by the upper radiator hose, where it is connected to the engine, driver’s side of the car. Simply buy another switch and do the same resistance test on your meter. Again if the switch reading is way off, replace it. This switch can also interrupt the signal your AC compressor. If this switch is good…
6) You will need to check out the AC evaporator Sensor. Located on the front passenger side of the console. You will see a panel that needs to be removed. Using an screw driver or a plastic panel prying tool, you will pry on the side closest to the rear of the car, the front part of the panel is held in with a slip type retainer, do not pull at the front of that plastic piece. You have to pry/pull only at the rearmost part…it will feel like you are going to break the panel. Inside you will see a wire and a connector that leads into the plastic box under the dash and in front of the console. You twist anti clockwise and pull the sensor out being careful not to damage the sensor (its basically a thermistor, or a resistor that changes it’s resistance value based on temperature.) To test the AC evaporator sensor, take a resistance reading at room temperature, put the sensor in the freezer for 10 minutes and take another reading. You should notice a big resistance swing between room temperature and the freezer temperature. If not replace it. Again this sensor will prevent the AC Compressor from getting the right signal to turn on.
7) Finally, if all this checks out, replace your AC Temperature Control Panel/Board. I have no test for this.

Note that these procedures should test and fix 90% of all your problems (I have not gotten into replacement of the expansion valve, clogged/leaking evaporator/condenser, bad condenser fan, or even the possibility that you may have a bad ECU…yes I’m sure that all the AC signals go through the ECU, but that is way beyond the do it yourselfer and I did not have access to the schematics or a bi directional scanner, which costs thousands of dollars!), it is general in nature so please don’t flame me for the oversimplification, this is a guide not a thesis on AC repair/diagnosis and operation!

BTW my problem was the Transducer switch! With the engine running and the AC on, I only got a 4volt signal at the compressor, when I unplugged the transducer, the AC fan went off, when I plugged it back in, the AC fan turned back on, so I mistakenly assumed that the switch was good!!! NOT!!! Hours and hours of work, and troubleshooting later, I bought a NEW transducer, compared my resistance readings as above, replaced the switch and vacuumed and recharged the Freon and SUCCESS!!!!

If you like my post, check out my Youtube channel, “howtoheaven”
 

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@ZFORCE

Here is a copy of the FSM that should contain the schematics that will help your how-to. It's a bit too involved for me or anyone else that hasn't dealt with a HVAC system before. Though I appreciate the effort!

It's too big to host anywhere other than google drive, so here's a link straight to the file from my google drive.

https://drive.google.com/open?id=1do13Aw-YttOjh1lPbtt8ohGxIw9FFc1e
 

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What was the transducer PN that you installed?

Did not find a youtube account for "howtoheaven"

But, I did find a PN for a 'clutch' on the front of my A/C compressor, even on a variable solenoid compressor
 

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The transducer is located in the high pressure line, and the VDC electronic control valve is in the back of the compressor. If the A/C delays producing cold air after start up, cold air warm at idle but when driving the system performs as it should.................99.9999999% compressor/electronic control valve (ECV).


Been through this and back in May with 123,000 miles, rather than changing the "ecv", replaced the compressor with a used unit, 2013 Sonata 24,000 miles. When done, 94 degrees/humid-41 degrees out of center vents and when car is stopped cold air continues. Today, 98 degrees and by the time I got the car turned around in the driveway, cold air, and with the settings 69/69 after a short period of time the auto fan started slowing down.



Did want to mention, there is no clutch on the VDC as the shaft turns continuously. In the old clutch style compressors, one could work on the system and then drive to a shop to evacuate and charge, but if one were to run the car with the VDC and no refrigerant, the compressor would surely seize as no oil would circulate throughout the system. When this happens the pins on the front of the compressor would snap to allow the engine/belt to operate, but the a/c system is done for and would require a great amount of work/replacement parts to function once again.


If one were low or out of refrigerant, don't use the car unless you get a belt to bypass the compressor.
 

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Ok I have a new compressor, proper refridgerant pressure, tested the evaporator sensor and it was good, still no ac, I guess next ima test the low press switch and the high pressure switch, any one know the proper ohms it should read while installed and car on?
 

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Just a question, after system evacuated, how do you know proper amount of refrigerant if no a/c?
Did you fill by weight, but the compressor needs to operate to draw in the gas.
 

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OK, short intro to a long post! My son bought a 2011 Hyundai Sonata. We noticed on test drive that the AC was warm at idle, we asked the seller, he disclaimed any AC problems and said it was normal. During the test drive, it cooled of at speed. A day after purchasing it that the AC would get really hot at Idle, work better at speeds...sometimes…and then it finally stopped cooling altogether, day 3 of ownership!!! Buyer beware~!

After hours of searching forums and youtube videos, NOBODY had enough information to solve this problem. So after researching this to death, I just went to work troubleshooting it and solved it myself! I may do a video explanation also on my Youtube channel “Howtoheaven,” in the future. Since I could not find any real help. I have decided to share my troubleshooting tips to help others that may have 2011 Hyundai Sonata AC problems. This is long, but to troubleshoot properly it is a must that you understand the components and general workings of this system. I cannot explain, on this forum, how to trouble shoot all problems, but this should help with the most common ones.

First, the 2011 Sonata was the first year to get the Variable compression AC compressor. This was a Toyota invention that I believe dates back to 1997, and is licensed to Hyundai, VW and I'm sure other manufacturers. It is a digital system!! So do NOT try and run 12v power line to the compressor!!! There is no Clutch Coil!

This is going to be long but hopefully comprehensive! I did not have access to schematics and just logically figured out the system by observation. I was once an HVAC tech.

Overview of the Components:

The main components are the AC controller (basically the switch panel with the fan/ temperature and mode switches mounted to it), the AC Compressor (which includes the AC controller valve, attached to it), the Transducer switch (aka pressure switch), which is connected to the high pressure line (the small line), the AC Expansion valve (it is attached to the fire wall, has a black plastic snap on cover, is aluminum, rectangular and has both the thick AC line {suction side/cold line}, and the thin AC line (pressure side/hot line) attached to it), the evaporator coil (mounted inside the dash and un-viewable), the evaporator temperature sensor (mounted at the front most, passenger side of the console, under a removable plastic snap on cover, and it plugs into the evaporator housing and is a twist and pull type sensor), and finally, the condenser (a radiator like aluminum unit mounted in front of the black Car Radiator, you can see the AC lines connected to it.).

In order to trouble shoot the system, you need to understand its components, so here goes!

What makes this system so hard to troubleshoot is that it is NOT an Analog AC System, it is a Digital System! The Compressor, compresses the Freon, variably. It does not have an AC clutch! And the compressor is always on! The pulley on the AC compressor looks like a standard clutch, but it is ONLY a pulley!!

The compressor has what is called a Swash Plate inside it. The Swash Plate is like a variable angled spinning disc, it changes the stroke of the compressor pistons, by changing the angle of the swash plate, thus, varying the compression and the amount of freon it pumps. This system was introduced to squeeze every MPG out of the car. A standard compressor is either ON or Off, the variable compressor is low and behold, VARIABLE, thus saving fuel…and wear and tear on the engine! It turns on and off based on a number of variables such as engine speed, temperature etc.

The brains of this system is the AC control board, which is mounted in the center dash AC controls. This board actually is where the fan, temperature, and mode switch are soldered to. My Sonata had manual AC controls, but I would bet that the dual climate control panel also has a logic circuit board mounted to it, and serves the same purpose of controlling the AC compressor, fan and mode switches, but is more adjustable for temperature.

The AC compressor has an AC controller valve that is replaceable and should measure between 10-14 ohms resistance. It has two wires coming off it, and is a pulsing power source (PWM pulse width modulated). A standard compressor only has one, +12v wire running to the coil. This AC controller valve is replaceable, but you must drain the Freon first, as the switch and compressor are under pressure. The AC controller valve is held in place by a single Snap Ring, that you remove, and then you just wiggle the AC controller valve, side to side and twist it to remove it. If you replace it, use some PAG AC oil to lubricate the o-ring before sliding the new one in.

So here is a super simplified explanation of how an AC system works! The AC system is basically a heat exchanger. In order to do this it needs a vehicle to move heat from one place to another. That vehicle is Freon. The brains of the system is the AC controller, not the one mounted to the compressor, but the control switch panel in the car. When you call for AC by turning the AC on and Turning the temperature to cool, the controller sends a signal to the AC compressor controller valve that then varies the angle of the swash plate according to how much cooling the AC controller and switches are asking for. The compressor pumps the Freon liquid to the AC expansion valve, which allows the liquid Freon to expand, changing it to a gas and super cooling it. The cooled gas then goes into the Evaporator radiator in the car and a fan blows the vehicle’s warm interior air over the super cooled coil. The air blowing over the evaporator exchanges the heat from the car and the super cooled temperature from the Freon gas. The cooled air is blown into the car and the heated Freon then flows out to the condenser, in front of the radiator, where the ambient air hitting the Condenser cools the heated Freon. The AC compressor then takes the gas and compresses it to a liquid again and the cycle continues again.

Ok so here is the troubleshooting!!

1) You need to determine if the AC compressor is running. You CANNOT do this by looking at the AC Compressor pulley and listening for a click! The easiest way is to connect AC gauges to both the high pressure, thin metal line on the car, remove the cap with the “H” printed on it, use the red hose on your gauges, and then connect your low pressure side, the thicker metal line, remove the cap with the “L” printed on it and use the green hose from your gauges. IF you have 134a gauges then you will find that the connectors are different sizes, so the quick connector only connects to the appropriate side. Turn on the AC at the control panel and watch the gauges, if the compressor turns on, you will immediately see both gauge needles move. Note, when the AC is turned off, the pressure in the system will equalize and the pressure should read about the same as ambient temperature on both the high and low gauge, i.e. if it is 85 degrees outside, both the low and high side pressures should read approximately 85 psi. If your low pressure gauge is nowhere near the ambient or room temperature (as explained above)…then it’s low and you need Freon and have a leak somewhere that needs to be fixed. When you turn the AC on, the low side pressure should drop to somewhere around 35-45 psi. The high side will go up over 150 psi. If you don’t have
2) If the compressor does not come on, meaning the pressures do not change at all or move a little and then stop moving (remember this system pumps pressure all the time, even when the AC is off….although it may only be a little), then you need to see if the compressor is getting power. To do this, depress the connector located on the compressor and pull the plug off….do this when the engine is off! The signal to the compressor is a digital Pulse width modulated voltage. Basically, a voltage pulse is sent to the compressor and more cooling required the more the pulsed voltage is ON. If your tool arsenal is large, you may have an oscilloscope that you can connect to the connector to see the pulses. If you only have a Volt meter (DVOM, like the free ones Harbor Freight gives away), just check for voltage. With the ignition on, but engine off (KOEO), you should get at least 10 volts. It won’t read 12 volts because remember, this is a pulse modulated system so your DVOM or meter is averaging the pulses, you should get approx. 10 volts. If you get 10 volts, then your AC Compressor control valve is probably bad and you can either drain your Freon and replace it alone, or you can drain your Freon and replace the entire AC compressor unit, that comes with a new valve, pull a vacuum, recharge your AC and your problems should be solved.
3) If you only have 4 volts, then you need to find out why the AC Controller is Not sending the right PWM signal to the compressor.
4) The first check should be you transducer switch also known as the Freon pressure switch/multi switch. It is located on the front passenger side wheel well on the high pressure/ small line close to the radiator. It has a plug on it that you push the retainer and remove. Do this with the power off. You must also drain the Freon to compare it to the new unmounted switch! If you don’t drain the Freon, then the pressure will give you a different reading than the new switch….you must compare apples to apples! Set your meter to read resistance and take readings from the 3 pins on the switch, and compare the readings to a new switch. If you don’t use/install the new switch, you should be able to return it. Make sure you check the readings between the first and last pin, the first and second pin and the second and third pin. Then compare it to the new switch. It should be easy to tell if the switch is bad as the reading will be way off. Pay attention to the meter, there is a huge difference between M ohms and K ohms (I won’t go into it but it’s huge). If this switch is bad, your compressor won’t get the right signal to turn on! If you replace it, remember to use some PAG AC oil to lubricate the o-ring before screwing the new one on and also use 2 wrenches, one on the line and one on the transducer…I actually used a 24mm socket on the transducer
5) If the Transducer switch is good, then check you Thermostatic Temperature switch, located by the upper radiator hose, where it is connected to the engine, driver’s side of the car. Simply buy another switch and do the same resistance test on your meter. Again if the switch reading is way off, replace it. This switch can also interrupt the signal your AC compressor. If this switch is good…
6) You will need to check out the AC evaporator Sensor. Located on the front passenger side of the console. You will see a panel that needs to be removed. Using an screw driver or a plastic panel prying tool, you will pry on the side closest to the rear of the car, the front part of the panel is held in with a slip type retainer, do not pull at the front of that plastic piece. You have to pry/pull only at the rearmost part…it will feel like you are going to break the panel. Inside you will see a wire and a connector that leads into the plastic box under the dash and in front of the console. You twist anti clockwise and pull the sensor out being careful not to damage the sensor (its basically a thermistor, or a resistor that changes it’s resistance value based on temperature.) To test the AC evaporator sensor, take a resistance reading at room temperature, put the sensor in the freezer for 10 minutes and take another reading. You should notice a big resistance swing between room temperature and the freezer temperature. If not replace it. Again this sensor will prevent the AC Compressor from getting the right signal to turn on.
7) Finally, if all this checks out, replace your AC Temperature Control Panel/Board. I have no test for this.

Note that these procedures should test and fix 90% of all your problems (I have not gotten into replacement of the expansion valve, clogged/leaking evaporator/condenser, bad condenser fan, or even the possibility that you may have a bad ECU…yes I’m sure that all the AC signals go through the ECU, but that is way beyond the do it yourselfer and I did not have access to the schematics or a bi directional scanner, which costs thousands of dollars!), it is general in nature so please don’t flame me for the oversimplification, this is a guide not a thesis on AC repair/diagnosis and operation!

BTW my problem was the Transducer switch! With the engine running and the AC on, I only got a 4volt signal at the compressor, when I unplugged the transducer, the AC fan went off, when I plugged it back in, the AC fan turned back on, so I mistakenly assumed that the switch was good!!! NOT!!! Hours and hours of work, and troubleshooting later, I bought a NEW transducer, compared my resistance readings as above, replaced the switch and vacuumed and recharged the Freon and SUCCESS!!!!

If you like my post, check out my Youtube channel, “howtoheaven”


Do you have to drain system to change the pressure switch or is there a check valve under nieth that prevents refrigerant lose
 
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