Cooling fan runs more often since a/c fix

[Rob Ward]

Had the a/c sensor fixed (i.e. moved) the other day so that the system no longer ices up after half an hour, but it seems that since that change the cooling fan comes on earlier and stays on longer than it did before. In fact, once the car is up to temperature, the fan is on pretty much constantly. Seems to come on as low as 190/191, and doesn’t go off again even when the temp drops to 187.

Also - and it’s always done this - the fan goes off immediately upon turning off the engine even if the temp is up around the 200’s. I would have thought that if the fan needed to be on for cooling then it would have stayed on few minutes after engine switch off. It does/has on my other cars.

Thoughts?

[TimMullen]

Sounds like the A/C compressor is actually running now like it's supposed to. From the Factory Service manual (you have downloaded the manual for the $25 haven't you?):

PL.3 - COOLING FANS & RE-CIRCULATION PUMP

The two cooling fans are fitted beneath the radiator or (with a.c.) condenser/radiator package, and the coolant re-circulation pump is mounted below the header tank. Both the fans and pump are controlled by the engine management ECU using data provided by the engine coolant temperature sensor mounted in the back of the cylinder head.

The cooling fans are switched as a pair, and will operate at half speed (connected in series) when coolant temperature reaches 98°C on rise, and switch off at 94°C on fall. If coolant temperature rises to 103°C, the fans will switch to full speed (connected in parallel), reverting to half speed at 98°C. The fans will also run at half speed, unless high coolant temperature dictates otherwise, when the a.c. is switched on and the compressor is running, or if the engine management system detects a fault with the inlet air temperature or coolant temperature circuits.

At road speeds in excess of 85 mph (135 km/h), equating to the fan stall speed, all fan functions are switched off.

Heat Soak

In order to help control engine temperature after switching off an engine whose temperature is over 88°C, the ECU will remain powered for a period of 20 minutes to allow heat soak management.

A coolant re-circulation electric pump is mounted below the coolant header tank and is plumbed into the heater supply line. When energized, the pump circulates coolant through the engine and heater system, drawing coolant from the back of the cylinder head, and pumping it through the heater matrix to the heater return pipe and back into the thermostat housing. The pump functions only with ignition off in conditions where the ECU remains live. The pump is then activated at coolant temperatures over 110°C, switching off at 100°C on fall. If temperature should rise to 115°C, the pump will be supplemented by the two cooling fans running at half speed, switching off at 110°C on fall.

[Rob Ward]

High pitched whining (were we all married to her?) instead of deep throaty burble, as requested.

Oh well. I'll just dream of DB9's.......

[EdHahn]

Originally Posted by TimMullen

<snip>
Heat Soak

In order to help control engine temperature after switching off an engine whose temperature is over 88°C, the ECU will remain powered for a period of 20 minutes to allow heat soak management.

A coolant re-circulation electric pump is mounted below the coolant header tank and is plumbed into the heater supply line. When energized, the pump circulates coolant through the engine and heater system, drawing coolant from the back of the cylinder head, and pumping it through the heater matrix to the heater return pipe and back into the thermostat housing. The pump functions only with ignition off in conditions where the ECU remains live. The pump is then activated at coolant temperatures over 110°C, switching off at 100°C on fall. If temperature should rise to 115°C, the pump will be supplemented by the two cooling fans running at half speed, switching off at 110°C on fall.

(Warning - thread hijack!)

I love it when real racing engineers design a car.

FWIW, at VIR two weekends ago, the ambient temps were in the low 80s - I never saw anything close to 110degC (230F) on the track or in the paddock. On track, I think I saw a peak of 196 degF, while in the paddock right after a session, the max temp I saw was about 200 degF.

ed

[Surferjer]

I was popping up to 218 pretty regularly autoxing on Sunday. Usually by the next run (co-driven) it would fall to 200. Fans running like crazy.

[Stan]

Jer...I was at 190 F....

[madguppy]

Rob,
can I ask who moved the A/C sensor?...dealer, local mechanic or yourself?

Im in Florida here and I love my Elise...but I can't stand this A/C!

I would sacrifice performance for a bigger unit but would even be happy for fixing the sensor as you have. Took a ride with my gf for an hour to Orlando the other day...we both almost had heat stroke.

Would appreciate all the "enthusiasts" just pass by this post...Im an American and I want my A/C!!

[daericks]

I live in Phoenix and my A/C is almost worthless during the day. Does anyone know how to get more out of this thing??

Dan

Originally Posted by madguppy

Rob,
can I ask who moved the A/C sensor?...dealer, local mechanic or yourself?

Im in Florida here and I love my Elise...but I can't stand this A/C!

I would sacrifice performance for a bigger unit but would even be happy for fixing the sensor as you have. Took a ride with my gf for an hour to Orlando the other day...we both almost had heat stroke.

Would appreciate all the "enthusiasts" just pass by this post...Im an American and I want my A/C!!

[etypeiii]

Originally Posted by daericks

I live in Phoenix and my A/C is almost worthless during the day. Does anyone know how to get more out of this thing??

Dan

If you are running with no top, I would say this is a hopeless dream. With top on, it is adequate in Las Vegas 110 degree heat. Phoenix is a bit hotter I believe.

With top down, it is ineffective and I would guess the unit would need 5x the capacity to be effective.

But in all fairness, many auto A/C units would not be effective with the top down in such conditions. I would never regularly drive any convertible in the summer, in the desert. (I just had to try it though with the Elise to see how it was.)

If the top was on, I would be surprised then that the A/C would be almost worthless. In 108-110 degree desert heat, I did not perspire at all wearing a light microfiber T-shirt and cotton shorts. No sweat on the seat faces, no damp shirt back. The A/C should be moderately effective in those conditions, if fully charged and healthy.



DLY

[Clinton]

The environment temperature is about 90F, the temperature at the vent is 65F, is this mormal? Or too high than it should be?

[Gregbj8]

I have a 2005 Elise with the sensor moved. At 82F ambient, the car temp at 190F+, my vent temp is 60F-64F. Pretty lousy A/C. The heater bypass mod I think will help by about 10F.

[Chris Mackey]

I live in Austin, Texas. Here's what worked for me, and I recommend them in this order:

1) Make sure the a/c is charged and operating correctly.

2) Make sure the coolant system is properly bled (instructions elsewhere on this forum). I bled mine and average engine temps fell from 204 to 194 F. It is about a 45 minute job and you will bust up your knuckles. However, the cabin is surrounded by coolant pipes and 10 degrees makes a BIG difference.

3) Tint the windows.

4) Consider the heater core bypass solution. It is a pretty quick to cut the hoses and reconnect them with a hose splicer. You live in Arizona or Florida or Texas, you don't need the heater, and it sucks anyway. If you MUST maintain the heater, put in Tonywa28's kit. Search the threads for it. It is worth about 5 degrees to me.

[TheViper]

Living in South Florida it looks like I have got my A/C to work great by making some numerous unconventional mods. Last year it was really bad.

[...m...]

Originally Posted by TheViper

Living in South Florida it looks like I have got my A/C to work great by making some numerous unconventional mods.

...details?..i think a total cooling overhaul will be my winter/spring project next year, before i have to sweat my way through another stifling summer...

[TheViper]

1)Tint all glass with “only” 3M Crystalline - Greatly reduced solar heat
2)Insulate side sills & front firewall on inside of the cockpit - Reduces convected heat from coolant, heater & oil pipes
3)Block the air inlets in the nose - Only use cooler recirculated air
4)Open up the driver’s side foot well recirculation inlet - Increases air intake air volume & results in substantial increase in air flow through vents into cockpit.
5)Replace the evaporator, capillary tube thermostat with an electronic version - prevents evaporator freezing

Originally Posted by ...m...

...details?..i think a total cooling overhaul will be my winter/spring project next year, before i have to sweat my way through another stifling summer...

[Gregbj8]

Chris...did you bypass your heater core by just splicing the hoses?
Are you worried about the lack of a heat sink thru the heater core if you bypass it permanently?

[Chris Mackey]

Originally Posted by Gregbj8

Chris...did you bypass your heater core by just splicing the hoses?
Are you worried about the lack of a heat sink thru the heater core if you bypass it permanently?

I used Toywa28's kit. If I went back in time, though, I'd just cut-and-splice. Living in Texas, there's no use for the heater.

I'm not sure what you mean in the second question. One thing that might be worth pondering is what happens to the heater core after water no longer runs through it. Of course, you'll lose that much water weight. I guess you could yank it, too.

[Gregbj8]

The heat sink part of the second question relates to Lotus designing the car to cycle coolant thru the heater matrix (I would think acting like a radiator) during hot engine shut down. My concern is that by straight bypassing the heater core you lose the "radiator" effect. I may be over thinking this.

[TheViper]

If you permanently by passed the heater core and you had certain engine related problems during the warranty period you run the risk of Lotus blaming it on the modification. Remember, after the engine is turned off and the temperature reaches 230'F the coolant recirculation pump comes on to cycle through the heater core.

[Chris Mackey]

Originally Posted by TheViper

If you permanently by passed the heater core and you had certain engine related problems during the warranty period you run the risk of Lotus blaming it on the modification. Remember, after the engine is turned off and the temperature reaches 230'F the heat sink pump come on to cycle through the heater core.

Lotus will probably blame either modification for any problems you have.

I guess if the heater core is an emergency radiator, permanently bypassing it might be a bad idea. I don't know what the odds of that is. I can't imagine the engine getting that hot unless it loses coolant...in which case the heater core is useless, anyway.