AC system logic or schematic question (pressure switch and rad fan) - Toyota Yaris Forums

rayfloyd170 · 08-29-2023, 12:54 AM

Hi to YarisWorld friends,

Good day.

I have a 3rd Gen 2016 Yaris Sedan 1.3MT 2NZ-FE

Last 2 weeks ago i topped-up R134a (with respect to ambient) and after that everything went well without any issues. I was checking both LP and HP and both were good within acceptable pressure range.

Yesterday, I was waiting for a phone call inside my Yaris for about 30min of idling with AC full blast. The ambient temp here in Saudi Arabia was around 43-45C or 109-113F and i noticed my coolant temp was rising and eventually going above 96-98C or 205-208F.

I was alarmed because suddenly the AC blower blows warm air and when i checked the rad fan it was not spinning at 98C or 208F. I checked the HP side of the AC system with a manifold and find it to be very high but below the threshold to activate the HP pressure switch ( reference 3.14 MPA of 455psi). I see only around 370psi in discharge, but it could be that my pressure switch is no longer calibrated hence it activated and shutdown the compressor.

But, here is my question.

If the AC compressor HIGH pressure switch is activated, does it also shut down the rad fan when temp is above 98C/208F?

Thats what happened in my case. I adjusted the refrigerant pressure to have a discharge of around 290psi and this immediately brought back the condenser/rad fan to high speed.

Condenser/rad fan motor is ruled out to be defective here since it is working at high speed.

I am not sure if this is the correct logic. Rad fan motor should continue to spin regardless of the pressure switch is activated or not. It should be dependent on the engine or coolant temperature if it reaches the setpoint of 96C/208F above it should cut-in to avoid possible engine overheating.

Please let me know your thoughts and in case there is a valid reference to this subject please share it with me. thanks

rayfloyd170 · 08-29-2023, 02:35 AM

I checked both fan no.1/2 relays and both were good, also checked the resistor showing 1.36 ohms i guess is within range.

i really dont know which is causing the strange thing to happen. i am left with probable cause only in my mind which is a worn-out carbon brush for condenser/rad fan motor, but is also unlikely because my condenser/rad fan still spins high speed.

i could not replicate that event anymore because i adjusted the refrigerant discharge pressure to about 290psi at ~43C ambient, that only happened when my discharge pressure was way too high above 370psi maybe.

For now, all is good, i tried to let the engine come to 96C with AC off and automatically comes in the high-speed condenser/rad fan.

Still looking for answer on my question above.

rayfloyd170 · 09-12-2023, 01:07 AM

Finally found the culprit. Case solved

My AC Pressure switch is acting weird. P/N 88645-60030

This P. switch controls the Magnetic Clutch for AC compressor and the Condenser/Rad Fan hence it has 4 terminals.

On a normal day it works flawlessly but when the AC compressor discharge pressure goes past 360-370psi it cuts off continuity to terminals 2-3 for the condenser/rad fan control thereby shutting down the condenser/rad cooling fan even when engine coolant temp is way high past 96C. It should cut supply only for the magnetic clutch as mentioned in the troubleshooting reference. Past 220psi it must have continuity for terminals 2-3 but mine cuts off intermittently about +360psi and goes normal below ~290psi.

Will be replacing them as soon as I get the denso replacement. i also need to evacuate the system and probably i will also replace the filter drier during that time.

08-29-2023, 12:54 AM	#1
rayfloyd170 Drives: Yaris 2016 1.3 Manual Join Date: Jun 2017 Location: SAUDI ARABIA Posts: 125	AC system logic or schematic question (pressure switch and rad fan) Hi to YarisWorld friends, Good day. I have a 3rd Gen 2016 Yaris Sedan 1.3MT 2NZ-FE Last 2 weeks ago i topped-up R134a (with respect to ambient) and after that everything went well without any issues. I was checking both LP and HP and both were good within acceptable pressure range. Yesterday, I was waiting for a phone call inside my Yaris for about 30min of idling with AC full blast. The ambient temp here in Saudi Arabia was around 43-45C or 109-113F and i noticed my coolant temp was rising and eventually going above 96-98C or 205-208F. I was alarmed because suddenly the AC blower blows warm air and when i checked the rad fan it was not spinning at 98C or 208F. I checked the HP side of the AC system with a manifold and find it to be very high but below the threshold to activate the HP pressure switch ( reference 3.14 MPA of 455psi). I see only around 370psi in discharge, but it could be that my pressure switch is no longer calibrated hence it activated and shutdown the compressor. But, here is my question. If the AC compressor HIGH pressure switch is activated, does it also shut down the rad fan when temp is above 98C/208F? Thats what happened in my case. I adjusted the refrigerant pressure to have a discharge of around 290psi and this immediately brought back the condenser/rad fan to high speed. Condenser/rad fan motor is ruled out to be defective here since it is working at high speed. I am not sure if this is the correct logic. Rad fan motor should continue to spin regardless of the pressure switch is activated or not. It should be dependent on the engine or coolant temperature if it reaches the setpoint of 96C/208F above it should cut-in to avoid possible engine overheating. Please let me know your thoughts and in case there is a valid reference to this subject please share it with me. thanks Last edited by rayfloyd170; 08-31-2023 at 06:21 AM.

08-29-2023, 02:35 AM	#2
rayfloyd170 Drives: Yaris 2016 1.3 Manual Join Date: Jun 2017 Location: SAUDI ARABIA Posts: 125	I checked both fan no.1/2 relays and both were good, also checked the resistor showing 1.36 ohms i guess is within range. i really dont know which is causing the strange thing to happen. i am left with probable cause only in my mind which is a worn-out carbon brush for condenser/rad fan motor, but is also unlikely because my condenser/rad fan still spins high speed. i could not replicate that event anymore because i adjusted the refrigerant discharge pressure to about 290psi at ~43C ambient, that only happened when my discharge pressure was way too high above 370psi maybe. For now, all is good, i tried to let the engine come to 96C with AC off and automatically comes in the high-speed condenser/rad fan. Still looking for answer on my question above. Last edited by rayfloyd170; 08-31-2023 at 06:23 AM.