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Discussion Starter · #1 ·
My 2007 Odyssey has always had an issue with poor air conditioner performance in hot conditions if the vehicle is parked or in stop-and-go traffic. This is really uncomfortable in the 6-month Florida summer, especially if the kids fall asleep and we need to idle in a parking lot for any time. A co-worker with a similar Odyssey has the same problem.

Here's information on a modification to the radiator/condenser fan control relays which improves A/C performance when the vehicle is moving slow or parked.

If you need more information, e.g. detailed schematics and pictures on the relay, let me know and I'll add it.

Adam
 

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On my DX model...(Canadian base model), when I put it on MAX AC, the radiator/condenser fan stay on all the time.

What happens when you switch it over to MAX AC?
 

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Looks like a great mod. Nice writeup.
 

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Discussion Starter · #4 ·
On my DX model...(Canadian base model), when I put it on MAX AC, the radiator/condenser fan stay on all the time.

What happens when you switch it over to MAX AC?
Max A/C didn't have this effect on my '07 EX-L. Believe me, we have to run on recirc/max mode all the time here in the summer.
 

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atoner,
This is a great mod! How hard is this to do, I mean, What are the chances that I can screw this up, and break something else?

I too have found that mid-day Florida heat is too much for the Ody when driving slow or idling.

I really like the idea of putting this mod on a switch, then pretty much all of the caveats you mentioned would be moot. One could engage the switch when driving slow, and disengage when not needed at highway speeds, or night time.

I use my remote starter several times a day, and when idling in mid day heat, the van only begins to cool down, until we starting rolling. With this mod, maybe the van will cool down faster when idling.
 

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Awesome mod.

Here's a thought. What if you could take input from the speed sensor and the light sensor and only do this while say you're below 25 MPH and in day time. Then, it would be a perfect mod but that's easier said than done. :)
 

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I tried the link to the website with the relay, and I get this:

"No records match your search criteria"

Digi-Key
 

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Dumb question, why not just take it off auto and manually turn up the fan speed? :huh:
They're talking about the radiator fans not the ones inside the cabin. I have noticed the problem being discussed personally. On very very hot days, even if you turn on the A/C at full blast and turn up the fan all the way and you're stuck in traffic, there isn't that much cold air coming out. Once you start doing 40+ mph, all's well in odyland.
 

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They're talking about the radiator fans not the ones inside the cabin. I have noticed the problem being discussed personally. On very very hot days, even if you turn on the A/C at full blast and turn up the fan all the way and you're stuck in traffic, there isn't that much cold air coming out. Once you start doing 40+ mph, all's well in odyland.
Ok, light bulb turned on...I get it.
 

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So this mod manually turns the radiator/condenser fans ON to generate air flow for times when the van is hardly moving forward?
 

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I read the DIY pdf file, I agree that it'd be better to install a switch on the dash that is under your control, i.e., turning it ON ONLY when you sit idle.
Otherwise your fan lifespan will be shortened quickly.

Anyway, this mod proves that this works! All you have to do is to install a switch somewhere.
Actually you can use the same mode but run the wire to the cabin and install a switch to ground.

The BMW engineers are smarter when it comes to this, after the vehicle reaches certain speed (such as above 15-20 mph or something like that), the Aux fan is shut off to prevent wear/tear on the Aux Fan.
 

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Discussion Starter · #13 ·
Does anyone have schematics for the speedometer? I'm guessing there's a digital bus which communicates to the instrument cluster (not easy to tap off a signal). There's a chance we could tap off an analog signal at the speedometer itself.

It may also be possible to tap off from the speed sensors at the wheels. Again, more effort that I wanted to put into the initial mod.

Now that it has cooled off here in FL, I'm going to disable the mod for the winter.

I would sleep better if I knew the fan wasn't coming on at highway speeds.

On my last car, I installed a switch under the dash to engage both fans at high speed. This was useful for the A/C at low vehicle speeds and to cooling off the engine bay if I needed to do work, but with the engine off it'd kill the battery quickly.
 

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Discussion Starter · #14 ·
I just wanted to report back that I've installed the fan mod for the 3rd summer with no ill effects. I'm still getting a fantastic improvement in cooling for city driving, idling in parking lots, etc. The AC cools down the vehicle much faster with the mod installed. I've had no issues with the radiator fans, cooling relays, etc.

For the past two years I've installed the relay around early June and taken it off around October.

Adam
 

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This is interesting because in my 2007 Ody LX, once the AC button is pressed On, the Low-Speed Feature is on (both Condenser and Rad Fan run at low speed). Maybe the O.P.'s relay failed to work to start with??? New relay is $4 at dealer.

Here is the schematic of Hi vs Lo Fan Realys:

 

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Discussion Starter · #16 · (Edited)
This is interesting because in my 2007 Ody LX, once the AC button is pressed On, the Low-Speed Feature is on (both Condenser and Rad Fan run at low speed). Maybe the O.P.'s relay failed to work to start with??? New relay is $4 at dealer.

Here is the schematic of Hi vs Lo Fan Realys:

As I described in my original PDF, my fans did behave as you state: both on low when the AC is on. Low speed isn't enough for cold AC if the van is stopped. I suspected this when the air was dramatically cooler once I got up to ~ 40 mph. That's what triggered the idea to have the fans come on fast with the AC.
 

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Interesting...

If you look at the electrical circuit, "FAN LO" from PCM triggers the "AC Condenser Relay", sending 12 V to both fans (the 5-prong relay default setting is current flowing from "1" to "4"). Now both fans are connected in series, this is why both of them run slowly as designed.

When the PCM sends "FAN HI" signal (when engine temp is too hot) to "Radiator Fan Relay", this does 2 things:
1. Uncoupling the 5-prong relay so the Condenser Fan stops.
2. 12V is sent directly to "Rad Fan" itself, therefore "Rad Fan" runs at HI speed.

PS: Although one fan is called "Condenser", and the other "Rad Fan", they sit side by side, so functionally, they should be called Aux Fan and simply runs LO or HI, and that is it. This is the terminology used in BMW, Volvo etc.
By calling these different names, Honda engineers made things more confusing for people.


 

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The other way to do this mod (so Aux Fan can run on HI on demand by driver) is:
- Locate the 5-prong relay underneath the PS Reservoir.
- Find Pin #3 and run a ground wire so one can control it by grounding it.
Once you ground pin #3, Aux Fan runs on HI.
 

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Discussion Starter · #19 ·
I would still love to find a way to make the fans come on high only when I'm stopped or, ideally, my vehicle speed is below ~30 mph. I haven't put much thought into this, but I wonder if there's a signal I could tap into. I'm guessing I could somehow get to the park signal from the shifter.

I've also noticed the headlights dim a bit when the fans are cycling due to the high instantaneous current drain. This may be another reason, in addition to fan and relay longevity, that Honda didn't bring the fans on high with the AC.
 
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