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Discussion Starter #1
Are the radiator fans on an '05 EX-L supposed to be dual-speed? If so, what triggers high speed?

Low speed = fans in series = 6V per fan
High speed = fans in parallel = 12V per fan

I ask because the A/C in my Odyssey is crap when the van isn't moving. It is fine at highway speeds. I have not seen/heard the fans go high-speed even when the engine is hot and the A/C is on. They always seem to be on at the same low speed.

I did some checking tonight, and both fans come on, low speed, with the engine on or off and the A/C on. If the A/C is off, the fans don't come on until the engine gets pretty hot, and then they only come on for a brief period. I couldn't get the fans to come on high by having the engine hot and the A/C on, but that may have been because it was hard to get the engine hot enough to trigger the fans based on engine temp alone.

I checked the fans and the relays. I can see where they are usually connected in series and powered through the A/C fan relay. I can see how they could be connected in parallel, and I can get the fans to go high-speed if I jumper around the relays. The relays check out fine, but I'm not 100% sure about the connections behind the relays. I don't have a wiring diagram and it was sweltering in my garage, so I gave up.

I had the recall work done for the transmission shudder. This was supposed to update the computer past the version which fixed a bug preventing high-speed fan operation, but I haven't seen a difference in A/C performance since then.


If this is a lame programming "feature" I'd feel comfortable rigging some relays, a thermostat, and some logic to make the A/C kick on the high speed fans when hot but ensure the fans still come on low speed for engine cooling, as long as the fans are able to handle 12V each.

Thanks,
Adam
 

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Don't have the 05 manual but from the 04 manual both fans come on in series with the condenser fan relay on ( controlled by PCM when AC on) and the Radiator fan relay off and the fan control relay off. If the coolant hits 210 degrees the radiator fan relay picks it will also pick the fan control relay and both fans will run in high speed. At 199 degrees the condenser fan relay will be picked by radiator fan switch A. These relays are controlled by a signal from the PCM through three diodes. If you plan on troubleshooting it I suggest you grt the OEM service manual so you can trace the paths with a meter.

If you feel the the fix they put on I would go back to the dealer and have them verify what they did.
 

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Discussion Starter #3
Thanks for the reply. It is actually an '07 EX-L (my typo) but it is from the same vintage as the '05.

I'm assuming Honda just didn't bother to have the fans come on high when only the A/C is on. Obviously they don't need to be on high all the time to keep the engine cool, but it really seems like having them on high would help a lot with the A/C. I know that a similar modification on my Pontiac Grand Prix helped the A/C when parked.

Any idea why it would be bad to have the fans on high more often? Just wear and tear on the motors?

I did check the charge, and it is right at the low end of the suggested range. It could probably use a little more charge, but it doesn't seem to be the main problem. The speed at which air moves seems to be the culprit.
 
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