Air conditioner questions

[Loppysaurusrex]

So I have no doubt that everyone here notices that driving manual with an SI while the A/C is running is less than a smooth experience, quick RPM drops with jerky clutch engagement and all that.

My question is, does the HP drain and RPM drops caused by the A/C change based on how cold you have the A/C running or is it the same regardless of temperature?

I find driving with A/C so annoying that I drive with the windows down 7/10 times even when it's extremely hot, makes me debate wanting to rip it out all together and shed some weight.

 

[stilletto]

You experience a loss in RPM when the AC Clutch engages. So yeah, the colder the setting, the longer the compressor runs.

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[Loppysaurusrex]

You experience a loss in RPM when the AC Clutch engages. So yeah, the colder the setting, the longer the compressor runs.

Sent from my SM-G930T using Tapatalk

So if I just have it on a little bit on the cool side it will be much more easy to manage?

 

[Flightmaster127]

This is common in almost every vehicle that has ac. I believe the compressor requires something like 5-10hp to run it under load.

 

[stilletto]

So if I just have it on a little bit on the cool side it will be much more easy to manage?

Possibly? I honestly couldn't tell you. I rarely turn my AC on in my Evo. Just open all the windows and race everywhere.

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[Loppysaurusrex]

This is common in almost every vehicle that has ac. I believe the compressor requires something like 5-10hp to run it under load.

So there's no difference in power sapping regardless of temperature settings?

 

[Flightmaster127]

So there's no difference in power sapping regardless of temperature settings?

If the compressor clutch is engaged it will be drawing the extra load. I imagine that the higher you have it set the longer the clutch will stay engaged as it cycles on and off as needed to keep the car cool. This will be notable around town but once your on the highway travelling at speed it will not. Regardless of how cool the setting is in the car its the outside temperature and the vehicles insulation that will determine how hard the system has to work to keep the interior cool.

 

[Loppysaurusrex]

If the compressor clutch is engaged it will be drawing the extra load. I imagine that the higher you have it set the longer the clutch will stay engaged as it cycles on and off as needed to keep the car cool. This will be notable around town but once your on the highway travelling at speed it will not. Regardless of how cool the setting is in the car its the outside temperature and the vehicles insulation that will determine how hard the system has to work to keep the interior cool.

It's not automatic climate control so idk how it would turn on and off on its own

 

[Flightmaster127]

It's not automatic climate control so idk how it would turn on and off on its own

The compressor cycles based on the system pressure and demand, automatic climate control or not.

Side question - are your windows tinted?

 

[Loppysaurusrex]

The compressor cycles based on the system pressure and demand, automatic climate control or not.

Side question - are your windows tinted?

Yes, 5 percent on sides and back with a 6inch 5% strip on the front

 

[Flightmaster127]

Yes, 5 percent on sides and back with a 6inch 5% strip on the front

I'm surprised that's not helping you keep some of the heat out as you lose a lot of your cooling through the heat transfer from the glass.

 

[Loppysaurusrex]

I'm surprised that's not helping you keep some of the heat out as you lose a lot of your cooling through the heat transfer from the glass.

Well I do live in Alabama where it's humid like a swamp

 

[tacthecat]

Well I do live in Alabama where it's humid like a swamp

Being a former Mobile Boy, I know what you mean. Swamp is the right term. When we visit we just run the AC hard - use recycle to de-swamp and then back it down as it slowly cools. Of course, be sure to open all the windows when you first get in, it's much easier on you and the car to blow out the 130+ degree air and get the "refreshingly cool" 95 degree air into the car first. Also when visiting in the Summer (April - October in Mobile) we take about a 4 mpg hit on our mileage (29 vs 33) but it's better than melting.

 

[NoMoreNissans]

lol if you think the AC ruins your Si driving experience, try blasting AC in a manual R18. I have to mash the gas pedal just to get it moving in first, and trying to do a slow rolling start in 2nd will almost make you stall

 

[Only Human]

On the US model Si with non-automatic A/C control, adjusting the hot/cold dial will not change the duty cycle of the compressor.

This is because, the evaporator will continue to have the same outside air passing through it. The outside air passes through the evaporator, or the heater core, or both before it reaches the cabin.

What WILL change the duty cycle of the compressor is the fan speed.

This is because, the compressor on/off state is determined by the temperature of the evaporator. When the evaporator temperature reaches the upper limit, the ECM turns on the compressor to bring it down. The slower the fan speed, the less volume of warm air passing through the evaporator, the slower the evaporator temperature rise when the compressor off.

The other reason why the hot/cold temperature dial won't affect duty cycle of the compressor is because, both the evaporator and the heater core are at the same stage of the HVAC. If the evaporator was before the heater core, the duty cycle would still depend on outside air temperature; if the evaporator was after the heater core, making cabin air "warmer" would just increase the duty cycle of the compressor because the evaporator would be receiving even warmer air than the outside. Neither of these cases are true.

However, also, the recirculation mode will lower the duty cycle of the compressor, once the cabin is cooler than the outside, because then, the cooler cabin air is passed through the evaporator instead of the outside temperature, reducing the demand on the compressor.