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Old 08-28-2013, 11:08 AM   #1
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Water/Tranny Fluid Temps Running Dash AC

I had an interesting "revelation" last weekend regarding water and transmission fluid temps when I turned on my dash AC. We were running the genny and house AC until late in the afternoon and then needed some cool air because we were west bound and the sun was heating us up in the cab. All day the outside temps were in the lower to middle 90s. I had been showing 199* water temp and 201*-207* for the transmission while cruising along. After turning on the dash AC to max but using a low fan setting the water dropped to 180* and transmission to 181*-186*. I wasn't expecting that at all.

The the simple question, "Is this normal?"

My first thought was that it might be possible that I was getting some leakage through the valve that controls water going through the dash heater. That would make some sense because the AC would then cool the water returning to the engine. I haven't noticed any overly warm air coming form

OTOH...perhaps the valve is suppose open a bit during use of AC?

One other thought...

It is my understanding that running at the higher temps is good because I *THINK* the engine works better at the higher end of normal temps. Any thoughts on that?
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Old 08-28-2013, 11:12 AM   #2
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If you have a diesel pusher, does the cooling fans speed up with the A/C on? That increased air flow may help with powertrain cooling.
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Old 08-28-2013, 11:23 AM   #3
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Common Practice

It's a common practice to have hot water going throught the heater coil all the time. It keeps them from corroding out sooner than they do.

Sometimes there is a valve that turns off the flow of hot coolant when the A/C is on.

My F250 A/C was barely adequate until I added a vacuum valve from a Ford Ranger to shut off the heater coil. What a difference! It will actually form ice crystals if left on long enough.

Or maybe engaging the A/C locked your fan clutch?
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Old 08-28-2013, 11:23 AM   #4
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Depending on the location of the A/C system condenser , and the program of the rad fan controller ( assuming side rad here ) when you went to Max A/C, the rad fan probably ran continually, bringing the temps down.
Even if the water valve were leaking; it should shut down completely on Max A/C; , I doubt that any cooling effect that the A/C had on the coolant in the heater core would show up on the temp gauge.
Diesel engines need to be at full operating temp for best combustion, I know there are minimum temps not aware of max, At least not in anything I've read so far.
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Old 08-28-2013, 11:24 AM   #5
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If you have a diesel pusher, does the cooling fans speed up with the A/C on? That increased air flow may help with powertrain cooling.
It is a thought but I'm not too sure about that. Once the water temp gets up to 199* I would think that fan clutch is fully engaged. At that point the only way the fan speed would increase would be with higher engine RPM.

Does that make sense?
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Old 08-28-2013, 11:27 AM   #6
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@199 the fan is probably not at high speed or (if you have) a fan clutch it is probably not locked yet. 199 I'd say is in the "normal" operating temp
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Old 08-28-2013, 11:30 AM   #7
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Depending on the location of the A/C system condenser , and the program of the rad fan controller ( assuming side rad here ) when you went to Max A/C, the rad fan probably ran continually, bringing the temps down....
Yep...side radiator. OK...maybe I don't fully understand the fan clutch and making a bad assumption that it would already be locked up.

If I understand what you are saying it is possible (maybe probable) that even at 199* the fan clutch still cycles on and off but then with MAX AC on it would then be lock up continuously.
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Old 08-28-2013, 11:48 AM   #8
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It is a thought but I'm not too sure about that. Once the water temp gets up to 199* I would think that fan clutch is fully engaged. At that point the only way the fan speed would increase would be with higher engine RPM.

Does that make sense?

Im no expert on these by any means but my thought would be as the other poster said, the fan is at a lower speed. My thought on this is there would need to be a higher speed available incase the engine gets hotter than normal to allow for more airflow to try and control the heat.
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Old 08-28-2013, 11:56 AM   #9
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Side Radiator/clutch

If it's a side radiator the fan (or fans) are probably electric. In that case the fans probably turn at an electrically controlled speed based upon temp/load and/or the phase of the moon.
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Old 08-28-2013, 02:21 PM   #10
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If it's a side radiator the fan (or fans) are probably electric. In that case the fans probably turn at an electrically controlled speed based upon temp/load and/or the phase of the moon.
Mine, and I believe most, side rad DP's use either a PTO or usually a hydraulic fan with a control module that takes engine water temp as well as AC usage as input to control fan speed. Perhaps they also take tranny temp into consideration as well.

Either way, I am with the others that your controller sets fan to max when AC is on. This brings about an interesting thought. There is a SIGNIFICANT impact to mileage when fan has to run at full speed (~70HP to fun just the fan). If the fan defaults to high when AC is on, would it be more efficient to just start the gen and run the coach AC and NOT run the cabin AC???

Thoughts?

Chris
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Old 08-28-2013, 02:53 PM   #11
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...
Either way, I am with the others that your controller sets fan to max when AC is on. This brings about an interesting thought. There is a SIGNIFICANT impact to mileage when fan has to run at full speed (~70HP to fun just the fan). If the fan defaults to high when AC is on, would it be more efficient to just start the gen and run the coach AC and NOT run the cabin AC???

Thoughts?

Chris
NORMALLY I don't run the dash AC. I have 2 big dogs and I use the coach AC systems to make sure they stay comfy in their crates. HOWEVER I was running the dash AC for direct air flow because the sun was in our face and heating us up enough to get uncomfortable. There isn't enough air flow from the coach's overhead AC vents that reaches us in those conditions. Make sense now?

Yep...I agree that running the dash AC is not my first choice either. I have read the same information and tend to think that running the genny is more fuel efficient than running the dash AC.

Yes, the fans are hydraulic. Also, (as I learned at Spartan) once it gets locked up on high the actual fan speed is controlled by engine RPM. That is why using higher RPM for climbs yields lower engine temps than climbing at lower RPMs.

So...if I understand the comments...What I am seeing is that the use of the AC locks up the radiator fan at high speed and thus the cooler running engine.
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Old 08-28-2013, 06:57 PM   #12
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So...if I understand the comments...What I am seeing is that the use of the AC locks up the radiator fan at high speed and thus the cooler running engine.
When running with just the normal A/C mode the rad fan may cycle to high with the A/C compressor clutch, when on Max A/C the fan could just stay on high , because the compressor clutch is rarely dis-engaged . When traveling with the cruise on , I have to depend on hearing the rad fan cycle , to know it's working. When I have my foot on the throttle , I can feel the fan cycle to high. Yep it's a drag on the system, and only two speeds on my old rig.
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Old 08-28-2013, 07:45 PM   #13
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If you run your gen for "whole house" cooling while traveling it's difficult to cool the drivers area. We bought a small squirrel cage fan (Lowe's has them) that is 110VAC and aim it at the drivers area. It helps alot without having to run the dash A/C too.
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Old 08-28-2013, 08:43 PM   #14
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If you run your gen for "whole house" cooling while traveling it's difficult to cool the drivers area. We bought a small squirrel cage fan (Lowe's has them) that is 110VAC and aim it at the drivers area. It helps alot without having to run the dash A/C too.
I do miss the defogging fans of my Winnebago that I could point at us. I was thinking I would try getting a fan like you suggested...THANKS!
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