So, my AC and electrical diagnostic skills go their workout today. I've figured out my problem but lets see if anyone else comes to the same conclusion. This post is for those that like a good electrical challenge and we'll see if you come to the same conclusion.
Vehicle:
2008 Odyssey Touring; 148K miles. VCMuzzler II installed.
Complaint:
AC doesn't get very cold at idle and warms up a bit when sitting at a traffic light or stop sign. When driving down the road the AC seems to be OK.
My initial diagnostic steps:
Connected my AC manifold gauges to the system and put the vehicle in the test condition per the manual for checking pressures and temps: Hood open; front doors open; put temp gauge in upper center vents and one near the recirc intake; Front/rear AC to max cool; vents on; fan on high; 1500 RPM. Let run for 10 minutes in test condition and take readings.
Here were the numbers:
Intake (ambient) temp: 80F
Vent temp: 65-70F (should be around 45-50)
High side system pressure: 350psi (should be around 200-250)
Low side system pressure: 43psi (should be around 27-35)
Symptom found: High and low pressures are too high
After a bit of looking through the manual one of the causes for pressure readings like this is reduced airflow through the condenser.
Likely cause found:
I could hear the fans running so it wasn't obvious at first. However, upon closer inspection I noticed that the radiator fan (on the driver side) was not running and the condenser fan (on passenger side was on high.) So, that's obviously not right. Upon further inspection I found that both fans would run fine in low speed mode but when the system called for high speed mode (triggered by the normal high pressure in the AC system) the condenser fan would go into high speed and the radiator fan shut down. Interesting. Expected result is both fans should go into high speed mode when the AC pressure reaches 221PSI (per the circuit description below.)
Attempt a fix:
I break out the manual and read up on how the system works:
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So, I find a section that troubleshoots the high speed fan circuit for both the radiator and condenser fan and start going through it.
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Initially, I don't even get through the first note. It says if only one fan is inoperative don't use this procedure and go to the symptom troubleshooting chart:
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In the fifth block down it lists my symptom and takes me right back to the section I was just at. That figures. I get to step 4 where it has me connect a jumper wire across pin 2 and 3 of the AC pressure switch. When I do this the condenser fan goes to high and the radiator fan does nothing. So, when it asks "Do the radiator and condenser fans run at high speed?" I say no and go to step 5.
Step 5 is "Jump the SCS line with the HDS. If anyone knows what this is doing I'd love to know. I'm guessing it's keeping the PCM powered somehow so as not to cause any sudden power issues but that's just a guess on my part. I obviously don't have the Honda Diagnostic Scanner that can do this. Is there another way to do it and what is the "SCS line?" This is mentioned in may other sections of the book. That's a side note question I'd love to have an answer to. I decide I don't want to risk damaging the PCM so I assume the wiring is good from the PCM to the AC pressure switch connector, as there's no reason to suspect otherwise. It's never been disturbed.
Out of desperation I even tried swapping condenser and radiator fan relays (they're the same) but no change. What the heck is wrong with my cooling fan system?
Below is the wiring diagram for this circuit.
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Vehicle:
2008 Odyssey Touring; 148K miles. VCMuzzler II installed.
Complaint:
AC doesn't get very cold at idle and warms up a bit when sitting at a traffic light or stop sign. When driving down the road the AC seems to be OK.
My initial diagnostic steps:
Connected my AC manifold gauges to the system and put the vehicle in the test condition per the manual for checking pressures and temps: Hood open; front doors open; put temp gauge in upper center vents and one near the recirc intake; Front/rear AC to max cool; vents on; fan on high; 1500 RPM. Let run for 10 minutes in test condition and take readings.
Here were the numbers:
Intake (ambient) temp: 80F
Vent temp: 65-70F (should be around 45-50)
High side system pressure: 350psi (should be around 200-250)
Low side system pressure: 43psi (should be around 27-35)
Symptom found: High and low pressures are too high
After a bit of looking through the manual one of the causes for pressure readings like this is reduced airflow through the condenser.
Likely cause found:
I could hear the fans running so it wasn't obvious at first. However, upon closer inspection I noticed that the radiator fan (on the driver side) was not running and the condenser fan (on passenger side was on high.) So, that's obviously not right. Upon further inspection I found that both fans would run fine in low speed mode but when the system called for high speed mode (triggered by the normal high pressure in the AC system) the condenser fan would go into high speed and the radiator fan shut down. Interesting. Expected result is both fans should go into high speed mode when the AC pressure reaches 221PSI (per the circuit description below.)
Attempt a fix:
I break out the manual and read up on how the system works:
So, I find a section that troubleshoots the high speed fan circuit for both the radiator and condenser fan and start going through it.
Initially, I don't even get through the first note. It says if only one fan is inoperative don't use this procedure and go to the symptom troubleshooting chart:
In the fifth block down it lists my symptom and takes me right back to the section I was just at. That figures. I get to step 4 where it has me connect a jumper wire across pin 2 and 3 of the AC pressure switch. When I do this the condenser fan goes to high and the radiator fan does nothing. So, when it asks "Do the radiator and condenser fans run at high speed?" I say no and go to step 5.
Step 5 is "Jump the SCS line with the HDS. If anyone knows what this is doing I'd love to know. I'm guessing it's keeping the PCM powered somehow so as not to cause any sudden power issues but that's just a guess on my part. I obviously don't have the Honda Diagnostic Scanner that can do this. Is there another way to do it and what is the "SCS line?" This is mentioned in may other sections of the book. That's a side note question I'd love to have an answer to. I decide I don't want to risk damaging the PCM so I assume the wiring is good from the PCM to the AC pressure switch connector, as there's no reason to suspect otherwise. It's never been disturbed.
Out of desperation I even tried swapping condenser and radiator fan relays (they're the same) but no change. What the heck is wrong with my cooling fan system?
Below is the wiring diagram for this circuit.
