Mechanics

AIRCON FAN STAYS ON AFTER ENGINE SHUTDOWN

1998 Honda Accord

Air Conditioning problem
1998 Honda Accord 6 cyl Front Wheel Drive Automatic 195000 miles

This has happened recently as the weather has got warmer. After engine shutdown the air con fan (the B fan I think) stays on. It eventually shuts off after 15 mins or so but even though this may be a helpful feature (built in perhaps) to help cooling after heavy running, 15 minutes of fan running after shutdown seems excessinve and is danger of taxing the battery I would think. The aircon refirgernat is charged ok, the car is kept cool with the air con on so everything with the aircon seems otherwise ok. The car engine temperature remains constantly within an acceptable range and does not overheat. Outside air temp is 23-25 degs celsius so we are not talking desert tempartures here. Any clues?
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Lord farringdon
December 30, 2008.




The fans are controlled by the PCM .. perhaps the temp sensor is the problem .. sending wrong signal to PCM


http://www.2carpros.com/forum/automotive_pictures/266999_fan_3.jpg

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Dave H
Dec 30, 2008.
Hi lord farringdon,

Yup, I agree with Dave about the sensor.

Another possibility is shortage of coolant in the system.

KHLow2008
Dec 30, 2008.
Thanks for your responses guys. My mistake though. It's not the aircon (compressor ) fan which runs on but rather the radiator fan. My bad! Don't worry, I've already kicked myself up the backside several times for wasting your time on that one! : )

The funny thing is when I checked the temperature gauge the first time this happened everything was normal, hence my earlier comments. Today the engine temperature was way up and the problem occured again when I shutdown. I was towing a lightly loaded trailer up steep hills at the end of my journey and the outside air temp was about 25 degrees celsius. Even so this operational profile has not caused this problem in the past so something is certainly different.

I checked the coolant as you suggested KHLow2008. The coolant is full, no leaks and the anti-freeze is in good shape. I wonder if the thermostat is playing up? I also wonder if I got the ratio of anti-freeze to water correct the last time I changed the anti-freeze? With the weather getting warmer the radiator may not be as efficient if there is too much anti-freeze. Have you heard of this problem occuring at 25 degrees C?

I will also follow the temperature sensor path as you have both suggested. I'll let you know how I get on.

Thanks for your help guys.

Tiny
Lord farringdon
Dec 31, 2008.
Hi lord farringdon,

With a sore backside you won't be able to sit too long and enjoy a few beers to celebrate the New Year ; )

Towing would increase the temperature but the cooling fans should be able to handle it unless the cooling system is inefficient.

Possbilities of inefficient cooling are
1. Coolant, mixture out of specs
2. Thermostat, not opening sufficiently.
3. Clogged radiator
4. Weak water pump.
5. Clogging in other coolant passages.

HAPPY NEW YEAR

KHLow2008
Dec 31, 2008.
Further to this problem: Under standard driving conditions the cooling system operates normally but once I start to drive up any lengthy hill (say a kilometre or more) the car begins to overheat (temperature gauge goes from just above a quarter to 3/4) very quickly. If I turn the aircon off, the temperature slowly returns to normal even if still going uphill. If I drive the car without the aircon on, the car does not overheat regardless of operating on the flat or on hills. The problem has arisen since the weather in New Zealand has got hotter, although that might be co-incidence. (NZ is right hand drive, all distances are in kilometres and I think Accord in NZ = Acura in US).

Things I have noticed associated with the problem: If I don't notice the temparture rise (as I said it happens quickly) my first indication is that the aircon looses its cooling effect like some sort of switch has recognised the need to automatically turn off aircon to help the engine cool itself.

If I turn the car off when it has overheated, the radiator fan comes on for several minutes after engine shutdown. I think this is what it should do to help cool the engine down.

Car Details: Car: 1998 Honda Accord VTI-L 3.0 V6
VIN: 7A3CG1640WNVG 0066
ENG: J30A113385530
Mileage: 200,340kms

Things I have done so far: When the problem occurs I have stopped the car, left the engine running, opened the bonnet and checked that both fans are working. No problems there, but of course I don't know if one or both fans momentarily did not work (causing overheat) then started again so that by the time I have stopped the car and checked under the bonnet that are happily spinning. Due to the potential of expensive engine damage I am reluctant to continue to operate the car in the overheated condition just to just see if by chance the engine will cool again all by itself as a result of intermittent fan operation.

As explained above, the radiator fan also comes on after engine shutdown when the motor is overheated. In addition, I have noted the aircon fan starting with engine start (and aircon on). It seems the fans are both working as expected.

I have checked the coolant level at cold. Coolant is 50/50 antifreeze and has been relpaced recently. I can confirm the radiator is full to the neck and the header tank has fluid to the minimum mark. There are no leaks and the coolant level remained constant (no top ups required) before and after its replacement.

I have checked the radiator and condensor fins and there are no obvious signs of external blockage or damage that might affect cooling.

I have replaced the thermostat with an OEM part and have also replaced the water pump. I have noted the condition of the antifreeze which was very good and also the cleanliness of the internal passages at the water pump, thermstat and radiator filler neck entrances. There are no signs of any corrosion. I suppose there could still be an internal blockage but it seems unlikely given the shiny/clean nature of all the interanl passages I can see.

I have replaced the radiator cap with an OEM part.

I have replaced the fan control module and have also replaced the radiator and condensor fan relays.

The only items left to replace are the temperature control switches A and B and the engine coolant temperature (ECT) sensor although I think the ECT sensor is unlikley to be the culprit. I say this because the temperature gauge indications of engine overheating, seem to be supported by the fan going on after engine shutdown. The check engine light has not come on either which might be expected if the sensor was faulty. Am I wrong?

If the problem is with one of the temp control switches, which one is it likely to be? A or B and which one is A and which one is B. I don't want to replace more needless parts. Am I on the right track or is the overheating simply a sympton of something a miss in the aircon system? The engine remains at normal operating temparture with the aircon off so could this in fact be a problem with the aircon system for eg, might there be an internal blocakge in the condensor? Does refrigerant block condensor passages?

Thanks for the assistance so far.

Any further help would be most appreciated.

Regards

Terry

Tiny
Lord farringdon
Feb 5, 2009.
Hi Terry,

In US, Accord, Civic, Passport, Odyssey, CRV and Prelude are under Honda. Acura have Legend, Integra, TL, MDX and NSX.

The A/C would cut off when engine temperature exceeds a certain preset value.

The radiator fan is supposed to work at ignition off when the tempearture at the outlet of top radiator hose exceeds the preset switch temperature.

You do have an overheating problem and that is the reason the fan comes on after ignition switch is turned off. When engine ovrheats under strenous conditions, the cause is insufficient cooling. With the A/C on, there is additional strain on the engine and that would increase the heat produced by the engine operations, it should not be the cause. You have replaced most of the cooling system components so there are not many items left to check.

Since both fans are working, it should not be anything to do with the ECT sensor or fan switch, ( You have mistaken the ECT with the temperature gauge sending unit?) ECT fault would cause CEL or starting and performance faults. The Fan switch B is the one responsible for the fan operations at ignition OFF.

The sending unit is only an indicator for the gauge and it is working correctly since it is registering overheating, which is happening.

2 things that you should check.
1. Check for kinking of radiator hoses restricting coolant movement?
2. Did you check the radiator core for clogging? Did you drain off a little coolant from top of radiator and visually inspect the internal core for clogging? With A/C off, run engine till operating temperature and when fan comes on, feel the heat of the fan motor from various portion of the radiator. If any portion seems colder than the others, there could be partial clogging?

Did you use different brands of coolant for the system? Mixing of coolant would cause clogging of the radiator core.

KHLow2008
Feb 6, 2009.
Thanks KHLow2008 for the confirmations and clearing up of some of my statements.

Yes, I'm a little confused about the ECT versus the temperature sending unit. Are they two different sensors? Does the latter provide information for gauge readings and the former information to the computer? What can you tell me about " switch A" and " switch B". You say switch B is the one responsible for the fan operations at ignition OFF. Is that the switch near the thermostat? What does 'switch A' do and where is it located?

I have done as you suggested and checked to make sure there is no kinking or misalignment in the radiator hoses. When I had everything apart and coolant drained for the water pump and thermostat replacement I was able to see into the radiator filler neck and couldn't see any condition which even vaugally looked like rust or corrosion on the top of the fins. Coupled with the condition of visible surfaces and passages around the thermostat and the water pump, the general impression I got was a very clean water system. Still, one can't see much at all down the filler neck so one can only really make an educated guess based on what can be seen. So, I can't discount there might be something clogged in there. I will try your suggestion for feeling the temperarture of the airflow around the fans to see if that indentifies anything. In the meantime, anything you could tell me about the fan switches A and B (the only things I haven't replaced yet!) Would be most appreciated. Are they immersed in the coolant or are they simply resting on metal and taking block temperatures.

Regards

Terry

Tiny
Lord farringdon
Feb 8, 2009.
Hi Terry,

Yes, you are correct about the functions of the ECT and sending unit.

Switch A = On thermostat housing. Sends a ground signal to radiator fan control module when it heats up, at the same time activating the fan relay which would start the fan operations, when engine is running.

Switch B = On front of left cylinder head. It operates at a higher temperature than Switch A and when it contacts, it grounds the fan switch B terminal in radiator fan control module when engine is not running. This would inform the radiator control module to send power supply to the radiator fan relay which operates when the PCM grounds the relay coil circuit.

Both are immersed in the cooling system passages.

I have attached a wiring schematic for your perusal as I believe the previous one could be for a different model.


http://www.2carpros.com/forum/automotive_pictures/192750_FanCircuit98AccordV6a1_1.jpg




http://www.2carpros.com/forum/automotive_pictures/192750_FanCircuit98AccordV6a2_1.jpg


KHLow2008
Feb 8, 2009.
Hi KHLow2008. Thanks for that schematic which makes much more sense than the first one. Thanks also for the A and B switch explanations. Frankly, this tells me that the switches are operating as expected by turning the fans on and off at the appropriate times. What more could I ask for!

All things considered, and with nearly all the parts in the system replaced it really looks like the radiator must be the 'core' problem (ok, pun intended).

I tried out your suggestion of checking for cooler or warmer portions of air coming from the radiator but it all just seemed universilly hot. In addition, as I stated earlier in the thread, I had " checked the radiator and condensor fins and there are no obvious signs of external blockage", but your suggestions have driven me to go back there again and look a bit harder.

There is very little space between the condensor and radiator, you can't even get your fingers down there. When I originally looked down there I was looking for the obvious obstructions like a plastic bag, newspaper or build up of leaves that would cause a severe restriction of airflow, but as I said there was nothing obvious. On your suggestion I have looked more carefully and have noticed what appear to be darker patches on the external fins covering about 30-40 percent of the radiator. An even closer look suggests these patches might be consistant with build ups of insects, grass, dust etc actually inside the fins. I can't be sure until I get the radiator out but there does seem to be some foriegn matter there alright.

So, I'm hopeful we might have found the problem. (Fingers crossed). Now I can't do the job untill this weekend. In the meantime, if the radiator is in fact clogged in this way, what is the best method for cleaning those fins out once I have the radiator out? I have a small compressor but its old and pretty shot so I don't expect it to have much blow. Can I put the radiator in any kind of 'bath' to dissolve any buildup?

Thanks

Terry

Tiny
Lord farringdon
Feb 10, 2009.
Hi Terry,

You do not need very high pressure to get the grime or dirt etc off. Soaking it in a bath would be the best option but you must not use any substances that are too acidic. Dishwashing liquid would be a good choice for the soaking to soften the grime before cleaning.

Before soaking, use compressed air to clear off as much dust as possible to reduce the layers of dust.

We should be on our final stretch to victory.

KHLow2008
Feb 10, 2009.

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