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Discussion Starter #1
I drive a 2012 MDX with ~150K miles. Last summer, on a long road trip, the AC started to "die". The drivers side/rear vents started to blow less and less air, then the passenger side went. I couldn't get any air to flow through the vents. We parked the car at our destination, and tried again 2 days later, and everything worked normally.

I now notice that the drivers side gets a bit less air compared to the passenger side, and 3-4 hours into a drive, the air starts to die. I replaced the cabin filter right before this issue started, but have since replaced it again.

I've read some other threads but it sounds like their issues start as soon as the car turns on, versus a delayed issue.

Suggestions?
 

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Our 2001 MDX had similar symptom on recent 300 mile trip, high temps and humidity day. Thought at first blower was failing, then shut A/C off for a few miles, set controls to outside fresh air, then put A/C back on. Nice cooling resumed. Then I remembered other cars doing same - ICING of the A/C evaporator inside the dash. There is a sensor that is supposed to switch off A/C compressor when the evaporator develops ice, which then blocks airflow. If the sensor fails, the compressor keeps cooling and icing can completely block airflow. I'm told by a good A/C tech that the sensor is actually in or close to the evaporator in the MDX, buried 6 hours labor deep to remove dash to get to it. Poor man's approach is just shut the A/C off for a few minutes, run fresh air through the system, when good airflow resumes, you can resume A/C use. If this is your problem, permanent fix requires replacing the sensor switch.

No guarantee this is your problem, but as I remember it's a pretty common failure in auto A/C systems.
 

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Discussion Starter #3
Thank you!! This sounds exactly like our situation - the air does start working again if we let things hang for a bit. Also, searching A/C Evaporator sensor has given me some other threads to review...

The real question is to fix or just deal. Ha!
 

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@misstopsail, did you check to see the pressure in the system? being a '12 model year, I believe you are still R134a. Get a gauge on it, test it to present atmospheric conditions and see if you are under pressured. I would imagine your condenser fan turns on with the AC on? Also, do you see condensation drip under the vehicle? If the fan does not come on, you are not extracting the heat and it will also be an issue.
Fords, esp the Escape, had an issue with the system where the line pressure was exceeding and the system turned off. I have taken my '10 on longer journeys with the AC on and had no icing issues. Normally our drive is between 9.5 to 11 hours a stint.
 

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Yep, it's icing up for sure, I agree with the postter above who recommended you get the R134 level checked to make sure it's in spec...
 

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@smufguy - I have not, but can take it to the dealer. There is condensation drip usually - is that not normal?
The water (condensation from the heater core in the cabin) dripping is normal and it is similar to the drain you will see in your own home AC unit. The only thing is, you wont see the water drip in your house as it travels down a tube and gets dumped outside.

If the cabin fan is operational (under Auto or manual mode) , then the question is; is there enough airflow over the heater core (in the cabin) to transfer the heat and blow cold air. Even under the lowest fan speed setting, the air flow is enough. Normal culprit is a dirty cabin filter, but you had addressed it so the fan is just fine (we hope).
- Turn the AC on and turn the fan on to see if you can hear the compressor engage. There will be a substantial draw in engine power under idle, so you will notice a change in the engine's RPM and voltage. Typically a 14.3V will drop to 14.1V/14.0V when the compressor kicks on and the engine is just idling in PARK. If you do not hear the engagement, then proceed forward.
- the next step is to turn on the AC and set it to the coldest setting and then turn the blower fan on to the highest setting (do not set to auto mode) to ensure that the settings are correct, and then inspect if the condenser fan is turning on. When the condenser fan comes on, there is a noticeable difference in the sound as the fans (both radiator and condenser) run at their max speed. The system automatically regulates the speeds of these fans. It will take some time for the condenser fan to come on. If the engine is already at operating temp, then it will be on immediately.
- If the fans operate fine, then you need to check the system pressure to current atmospheric conditions. Invest in a $20 R134a refill can with a guage on it (like Below). The instructions are simple and the operation is straightforward. Clamp it on to the fattest of the two AC lines (marked with a 'L') and turn the dial to the current temperature and see if the pressure in the system is where it should be. Too much or too little refrigerant in the system will render the system inoperable and thus the AC compressor will not engage. If the compressor does not engage, then no AC.



If all the above checks out and you still have an issue, taking it to a trusted mechanic who is licensed to do AC recharging will be able to guide you in the right direction.

Case in point, my '16 Civic's AC stopped blowing cold air. The compressor kicked in, but since this uses the new R1234yf refrigerant I dropped it off at the dealership (mind you my car is only 2 years old). They found two bad O-rings and a leaking system with low pressure. Changed the O-rings and recharged it and now its working just fine. This issue is very common in the '16 Civic, '17 Ridgeline and the '18 Odyssey, all new generation 1st model year vehicles; not the O-ring issue, but the AC not working issue. It varied from leaking O-rings to under pressurized system from the assembly line.
 

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Discussion Starter #8
@smufguy - thank you for the explanation! I actually took it to the dealer this morning... ‘freon’ was 1/2 what it should have been. They also replaced the relay. Could not find a specific leak though. Will keep an eye on it - driving 3 hours tonight so we’ll test it for sure.
 
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