AC intermittent ON/OFF problems

[dlanger2]

Hello fellas,
Help needed for the next problem:
2012 Sedan 3.8L 100000miles
AC intermittently blows ice cold or hot.
Usually with lower ambient temperatures, starts to blow cold air right away.
Sometimes needs 20-30min to start blowing cold.
Sometimes blows hot only.
If started to blow cod, it will remains cold till I finish my trip (10-30min).

Took the car two times to the dealership.
On the first visit, they said the Freon pressure is just a bit lower than needed and they filled it with die. Charged me 250$. Came back after two weeks but they couldn't find any leak, but said they filled a bit more Freon(((
Came back after 2 months and they "find" a tiny leak at the compressor and offered my to replace the compressor for 1600$ w/o any warranty that it will fix the problem.
What is really surprised me they couldn't tell me what exact pressure they measured in LO and HI pressure lines in both cases.

The problem occurs in both AC only and climate control mode.
No error codes.

I don't think I have a leak problem, as I still have ice cold air intermittently after about 5 months from the last visit to the dealership and the Freon hasn't escaped yet from the "tiny" leak at the compressor.
Started to troubleshoot by myself and here bellow my findings:
1) Have increased RPM in about +100 when AC turns ON. I can't confirm if the compressor is running as it is variable compressor.

2) Don't have the gauges right now, but the HI pressure side is still pressurized. Confirmed by pressing on the needle at the HI filling port.

3) Confirmed that the fan doesn't spin when AC turns ON (Only one fan for AC condenser and for the engine coolant). But does starts to spin when coolant temp. gauge in the middle (spins in low RPM).
Connected directly 12V to the fan and it started to spin like a helicopter - so no problem with the fan.
Suspected the fan controller - replaced - no change.

4) Put a hand on the HI pressure line when started the AC and it started to vibrate for a moment and then stopped - looks like compressor was starting to pump pressure, but stopped for some reason. Probably some safety feature related to the pressure in the system.
Looks like the fan doesn't spin when AC ON for the same reason. After that couldn't recreate the vibrating in the HI line. Looks like the compressor is halted or some safety feature is activated.

5) Disconnected the wire from the HI pressure sensor. It is 3 pins sensor (+5V, Ground and Voltage Signal).
Computer supplies 5V and GRD and measures the the voltage at Voltage Signal that changes according the pressure.
Measured on the sensor a shortcut between GRN and the Voltage Signal while the cable is disconnected.
According the formula in the attached print screen, it is impossible to have 0V at Voltage Signal. The minimum will be 370mV. I think then it is 0V, this is a way to ECU to know that there is some disconnection occurred. But then I would expect to some error.

I think, as the system is still under the pressure, it shouldn't shows this even though there is no 5V to the sensor.
First question: Is it enough to determinate that sensor is faulty? A new sensor is not so expensive, but I gave to bleed and to refill the whole AC system(((

6) Next steps:
a) I can bypass the sensor and to apply 5V directly to the Voltage Signal, but I learn that modern cars doesn't like to get maximum voltage signals. So I think I'll use two AA batteries to make around 3V and will apply it directly to the Voltage Signal and will try to start the AC
b) To find a way to measure voltage at the Signal while the cable is connected and car is running.
C) Will re-scan again with and without sensor disconnected.

Second question: What do you think about my troubleshooting so far and please recommend me other steps you have in mind to help me to resolve this problem.
Appreciate you time reading my post and have a blessed day!

Update: I connected two batteries in serial and had 2.6V. Connected it directly to the Voltage signal and turned ON the AC. Now I have fan working on high RPM, but AC blows to hat, but warm air. Now, I think it's time to measure pressures.

 

[mikec]

Your debugging is better than what most folks think/do. With your AA battery setup, run the AC again and feel the hoses. See if the smaller hose from the compressor gets hot. If so, the compressor is running and there is at least a reasonable amount of refrigerant (not Freon, that's the old R-12 stuff). That hose should run to the front of the car, to the condenser (radiator-like thing). From there, another refrigerant line runs to a metal block bolted to the firewall pretty much dead-center and above the engine. That's the expansion valve assembly. One pipe should be warm, one should be pretty cold. The cold one will go back to the compressor in the larger (low pressure) pipe.

If the compressor output hose is hot, and the expansion valve output is cool/cold, assume the basic AC stuff is working. The problem is underneath the dash. There are small diverter doors driven by small electric motors to direct airflow across the AC evaporator or across the heater core. If those fail... you get heat. At least when the engine is warmed up... if you get ambient air temp with the AC on right after starting the engine - before the engine warms up - and then it gets hot I would suspect the blend valves. If the air coming from the vents is warm/hot before the engine can warm up (and the car has not been sitting in sunlight for hours, cooking the dash) then the AC system itself is likely the problem. I would suspect the expansion valve has "gone stupid" to use a friend's term. If that were the case you would have similar temperatures on the expansion valves in & out pipes. Give the square metal expansion valve case a couple good whacks; if that makes a difference then get a new valve. Which of course means draining the system of refrigerant first. Good chance to replace that faulty pressure sensor too.

That pressure sensor... unless you have +5volts and ground powering it, I would not trust the "0 volt" reading. If you had zero ohms, on a x1 scale (analog meter) or 200 scale (digital meter), between the ground pin and the output pin, that would be concerning and probably does indicate a fried sensor. To protect the rubber AC hoses and the compressor, pretty much all AC systems have pressure monitoring capability. If the pressure gets too high (blockage in the system downstream of the compressor, hot day, too much refrigerant, not enough airflow over the condenser due to leaves/crud accumulating and/or bad fans) the computer cuts power to the compressor drive. If the pressure is too low when the AC system is OFF the computer will prevent the compressor from engaging because low refrigerant pressure = low refrigerant quantity = the oil suspended in the refrigerant is gone too so the compressor would get shredded if it tried to run.

The best diagnostic is a basic gauge set. Serviceable ones are not that expensive and will tell you quickly if:
a) the refrigerant level is very low (the gauges will both show rather low pressure readings)
b) if there is a blockage in the system (high pressure gauge will go too high, low pressure gauge will go too low)
c) if the expansion valve is jammed fully open, doing nothing. The high pressure won't be very high, the low pressure won't be low. In fact, the pressures will probably be close to equal.

A local AC repair shop can probably handle everything for much less than dealer cost, especially if you find a locally owned shop rather than one of the chain stores. The overall "theory of operation" between various car makes and models does not vary all that much when it comes to AC systems since they have to use one of a small choice in refrigerants. Individual parts can vary considerably, like temp and pressure sensors... but the overall logic diagram and flowcharts are similar.

mike c.

 

[dlanger2]

Your debugging is better than what most folks think/do. With your AA battery setup, run the AC again and feel the hoses. See if the smaller hose from the compressor gets hot. If so, the compressor is running and there is at least a reasonable amount of refrigerant (not Freon, that's the old R-12 stuff). That hose should run to the front of the car, to the condenser (radiator-like thing). From there, another refrigerant line runs to a metal block bolted to the firewall pretty much dead-center and above the engine. That's the expansion valve assembly. One pipe should be warm, one should be pretty cold. The cold one will go back to the compressor in the larger (low pressure) pipe.

If the compressor output hose is hot, and the expansion valve output is cool/cold, assume the basic AC stuff is working. The problem is underneath the dash. There are small diverter doors driven by small electric motors to direct airflow across the AC evaporator or across the heater core. If those fail... you get heat. At least when the engine is warmed up... if you get ambient air temp with the AC on right after starting the engine - before the engine warms up - and then it gets hot I would suspect the blend valves. If the air coming from the vents is warm/hot before the engine can warm up (and the car has not been sitting in sunlight for hours, cooking the dash) then the AC system itself is likely the problem. I would suspect the expansion valve has "gone stupid" to use a friend's term. If that were the case you would have similar temperatures on the expansion valves in & out pipes. Give the square metal expansion valve case a couple good whacks; if that makes a difference then get a new valve. Which of course means draining the system of refrigerant first. Good chance to replace that faulty pressure sensor too.

That pressure sensor... unless you have +5volts and ground powering it, I would not trust the "0 volt" reading. If you had zero ohms, on a x1 scale (analog meter) or 200 scale (digital meter), between the ground pin and the output pin, that would be concerning and probably does indicate a fried sensor. To protect the rubber AC hoses and the compressor, pretty much all AC systems have pressure monitoring capability. If the pressure gets too high (blockage in the system downstream of the compressor, hot day, too much refrigerant, not enough airflow over the condenser due to leaves/crud accumulating and/or bad fans) the computer cuts power to the compressor drive. If the pressure is too low when the AC system is OFF the computer will prevent the compressor from engaging because low refrigerant pressure = low refrigerant quantity = the oil suspended in the refrigerant is gone too so the compressor would get shredded if it tried to run.

The best diagnostic is a basic gauge set. Serviceable ones are not that expensive and will tell you quickly if:
a) the refrigerant level is very low (the gauges will both show rather low pressure readings)
b) if there is a blockage in the system (high pressure gauge will go too high, low pressure gauge will go too low)
c) if the expansion valve is jammed fully open, doing nothing. The high pressure won't be very high, the low pressure won't be low. In fact, the pressures will probably be close to equal.

A local AC repair shop can probably handle everything for much less than dealer cost, especially if you find a locally owned shop rather than one of the chain stores. The overall "theory of operation" between various car makes and models does not vary all that much when it comes to AC systems since they have to use one of a small choice in refrigerants. Individual parts can vary considerably, like temp and pressure sensors... but the overall logic diagram and flowcharts are similar.

mike c.

Mike, Thank you very much for your detailed explanation.
Looks like I have more steps to follow.
Will update according my advance.

In regards of the suspected pressure sensor, I measured the resistance between the GRD and the output pin. Sorry, wasn't clear enough).
So I measured 0 ohm when the sensor is not energized. Thank you for conforming that pressure sensor is being used to protect the system.

On my way to buy the gauges.

 

[G-162812]

Hello fellas,
Help needed for the next problem:
2012 Sedan 3.8L 100000miles
AC intermittently blows ice cold or hot.
Usually with lower ambient temperatures, starts to blow cold air right away.
Sometimes needs 20-30min to start blowing cold.
Sometimes blows hot only.
If started to blow cod, it will remains cold till I finish my trip (10-30min).

Took the car two times to the dealership.
On the first visit, they said the Freon pressure is just a bit lower than needed and they filled it with die. Charged me 250$. Came back after two weeks but they couldn't find any leak, but said they filled a bit more Freon(((
Came back after 2 months and they "find" a tiny leak at the compressor and offered my to replace the compressor for 1600$ w/o any warranty that it will fix the problem.
What is really surprised me they couldn't tell me what exact pressure they measured in LO and HI pressure lines in both cases.

The problem occurs in both AC only and climate control mode.
No error codes.

I don't think I have a leak problem, as I still have ice cold air intermittently after about 5 months from the last visit to the dealership and the Freon hasn't escaped yet from the "tiny" leak at the compressor.
Started to troubleshoot by myself and here bellow my findings:
1) Have increased RPM in about +100 when AC turns ON. I can't confirm if the compressor is running as it is variable compressor.

2) Don't have the gauges right now, but the HI pressure side is still pressurized. Confirmed by pressing on the needle at the HI filling port.

3) Confirmed that the fan doesn't spin when AC turns ON (Only one fan for AC condenser and for the engine coolant). But does starts to spin when coolant temp. gauge in the middle (spins in low RPM).
Connected directly 12V to the fan and it started to spin like a helicopter - so no problem with the fan.
Suspected the fan controller - replaced - no change.

4) Put a hand on the HI pressure line when started the AC and it started to vibrate for a moment and then stopped - looks like compressor was starting to pump pressure, but stopped for some reason. Probably some safety feature related to the pressure in the system.
Looks like the fan doesn't spin when AC ON for the same reason. After that couldn't recreate the vibrating in the HI line. Looks like the compressor is halted or some safety feature is activated.

5) Disconnected the wire from the HI pressure sensor. It is 3 pins sensor (+5V, Ground and Voltage Signal).
Computer supplies 5V and GRD and measures the the voltage at Voltage Signal that changes according the pressure.
Measured on the sensor a shortcut between GRN and the Voltage Signal while the cable is disconnected.
According the formula in the attached print screen, it is impossible to have 0V at Voltage Signal. The minimum will be 370mV. I think then it is 0V, this is a way to ECU to know that there is some disconnection occurred. But then I would expect to some error.

I think, as the system is still under the pressure, it shouldn't shows this even though there is no 5V to the sensor.
First question: Is it enough to determinate that sensor is faulty? A new sensor is not so expensive, but I gave to bleed and to refill the whole AC system(((

6) Next steps:
a) I can bypass the sensor and to apply 5V directly to the Voltage Signal, but I learn that modern cars doesn't like to get maximum voltage signals. So I think I'll use two AA batteries to make around 3V and will apply it directly to the Voltage Signal and will try to start the AC
b) To find a way to measure voltage at the Signal while the cable is connected and car is running.
C) Will re-scan again with and without sensor disconnected.

Second question: What do you think about my troubleshooting so far and please recommend me other steps you have in mind to help me to resolve this problem.
Appreciate you time reading my post and have a blessed day!

Update: I connected two batteries in serial and had 2.6V. Connected it directly to the Voltage signal and turned ON the AC. Now I have fan working on high RPM, but AC blows to hat, but warm air. Now, I think it's time to measure pressures.

Hello fellas,
Help needed for the next problem:
2012 Sedan 3.8L 100000miles
AC intermittently blows ice cold or hot.
Usually with lower ambient temperatures, starts to blow cold air right away.
Sometimes needs 20-30min to start blowing cold.
Sometimes blows hot only.
If started to blow cod, it will remains cold till I finish my trip (10-30min).

Took the car two times to the dealership.
On the first visit, they said the Freon pressure is just a bit lower than needed and they filled it with die. Charged me 250$. Came back after two weeks but they couldn't find any leak, but said they filled a bit more Freon(((
Came back after 2 months and they "find" a tiny leak at the compressor and offered my to replace the compressor for 1600$ w/o any warranty that it will fix the problem.
What is really surprised me they couldn't tell me what exact pressure they measured in LO and HI pressure lines in both cases.

The problem occurs in both AC only and climate control mode.
No error codes.

I don't think I have a leak problem, as I still have ice cold air intermittently after about 5 months from the last visit to the dealership and the Freon hasn't escaped yet from the "tiny" leak at the compressor.
Started to troubleshoot by myself and here bellow my findings:
1) Have increased RPM in about +100 when AC turns ON. I can't confirm if the compressor is running as it is variable compressor.

2) Don't have the gauges right now, but the HI pressure side is still pressurized. Confirmed by pressing on the needle at the HI filling port.

3) Confirmed that the fan doesn't spin when AC turns ON (Only one fan for AC condenser and for the engine coolant). But does starts to spin when coolant temp. gauge in the middle (spins in low RPM).
Connected directly 12V to the fan and it started to spin like a helicopter - so no problem with the fan.
Suspected the fan controller - replaced - no change.

4) Put a hand on the HI pressure line when started the AC and it started to vibrate for a moment and then stopped - looks like compressor was starting to pump pressure, but stopped for some reason. Probably some safety feature related to the pressure in the system.
Looks like the fan doesn't spin when AC ON for the same reason. After that couldn't recreate the vibrating in the HI line. Looks like the compressor is halted or some safety feature is activated.

5) Disconnected the wire from the HI pressure sensor. It is 3 pins sensor (+5V, Ground and Voltage Signal).
Computer supplies 5V and GRD and measures the the voltage at Voltage Signal that changes according the pressure.
Measured on the sensor a shortcut between GRN and the Voltage Signal while the cable is disconnected.
According the formula in the attached print screen, it is impossible to have 0V at Voltage Signal. The minimum will be 370mV. I think then it is 0V, this is a way to ECU to know that there is some disconnection occurred. But then I would expect to some error.

I think, as the system is still under the pressure, it shouldn't shows this even though there is no 5V to the sensor.
First question: Is it enough to determinate that sensor is faulty? A new sensor is not so expensive, but I gave to bleed and to refill the whole AC system(((

6) Next steps:
a) I can bypass the sensor and to apply 5V directly to the Voltage Signal, but I learn that modern cars doesn't like to get maximum voltage signals. So I think I'll use two AA batteries to make around 3V and will apply it directly to the Voltage Signal and will try to start the AC
b) To find a way to measure voltage at the Signal while the cable is connected and car is running.
C) Will re-scan again with and without sensor disconnected.

Second question: What do you think about my troubleshooting so far and please recommend me other steps you have in mind to help me to resolve this problem.
Appreciate you time reading my post and have a blessed day!

Update: I connected two batteries in serial and had 2.6V. Connected it directly to the Voltage signal and turned ON the AC. Now I have fan working on high RPM, but AC blows to hat, but warm air. Now, I think it's time to measure pressures.

so did the cycling switch fix your concern ?