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18 votes
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Can a car AC unit be run on just the car battery?

I can't give you numbers or calculations without some work, but I can tell you than energy is never free. Cars have an A/C compressor that is mechanically driven by the engine because this is the ...
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17 votes
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Is it okay or useful to run heat and AC at the same time?

You're meant to. In fact, in older cars, it was automatic when redirecting air to the window defroster. On this GM control, the far right position would activate the A/C compressor. Almost always, ...
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15 votes

Vehicle AC works initially, but after driving for a while (hour+), the airflow drops to the point being ineffective

The evaporator is the component of the AC system that gets cold. It is located after the blower in the passenger cabin. As it cools the air that is passing over it, moisture condensed on the cold ...
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13 votes

Can a car AC unit be run on just the car battery?

Well, Teslas (and presumably other all-electric cars) have A/C so it's not impossible, but A/C takes a fair amount of power. On the other hand, Teslas store a lot of energy. The A/C is something ...
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13 votes

Are A/C Control Panels Universal?

In a word No, not even close. Some are all mechanical, some vacuum, some completely electronic. some are combined with the infotainment device (radio) even the ones of the same type from the same ...
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11 votes
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How do final stage resistors fail?

There is no real point in doing a resistance measurement. BWM, like with most other stuff, decided to put more in there than you need. They have put active elements in there, that control the ...
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  • 464
11 votes

Is it okay or useful to run heat and AC at the same time?

Yes, it is useful, okay and won't cause any damage. The usefulness comes from the fact that the AC not only removes heat from the air, it also removes moisture from the air (because cold air can't ...
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  • 13.3k
9 votes

Can a car AC unit be run on just the car battery?

The short answer to your question is no. As @JPhi1618 noted, the compressor is mechanically driven. Without the compressor you don't have any cooling. The AC runs by changing the state and pressure of ...
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8 votes

Can a car AC unit be run on just the car battery?

Yes, this is possible. Several companies (VAG, BMW) have switched to AC units that are driven by electric motors. For BMW, this is part of their Efficient Dynamics strategy, where they'll switch the ...
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8 votes
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Does putting down the visors help defogging the windshield?

I think the visor is right… When you put the visors down (or at the "right" angle) they stop the airflow from the defroster vents from being able to move across the headliner. They may even deflect ...
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  • 14.2k
8 votes

Vehicle AC works initially, but after driving for a while (hour+), the airflow drops to the point being ineffective

Another answer but less likely the solution is that the inside temperature sensor is faulty or being obstructed causing the system to think it's already cool and turns the fan down and temperature up. ...
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6 votes
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Which knob setting best cooks the mold inside HVAC?

The reason for the odor is that water condenses inside the ducts when the AC cools the air. Though there are drains, there will still be enough moisture in the system to allow mold to grow. The ...
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6 votes

Measuring A/C refrigerant I got 96 PSI, is 96 PSI bad?

For an A/C system to be functioning correctly, you need: In the cabin: something to exchange cold (an evaporator) something to move air over the evaporator (the fan) a working blend door that allows ...
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6 votes
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What can I do to prevent my air conditioner from smelling moldy as the temperatures begin to rise?

You need to prevent the buildup of mildew in the system during the colder months, as that's what causes the smell. One trick I've heard is to make sure you run the A/C regularly (at least once every ...
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6 votes

Are A/C Control Panels Universal?

No. Sorry. Absolutely not. If you stay within the same marque/brand you might have half a shot. For instance, a Chevy Cruze HVAC module has a better chance of working in your Pontiac, as GM, Ford, ...
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  • 12.2k
6 votes

why condenser is placed before the radiator?

The condenser is placed earlier in the flow of air coming from outside as it needs to cool the gas rapidly and the radiator is not affected too much by slightly warmer air. The A/C condenser only ...
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  • 34.4k
5 votes

How can I determine my HVAC layout?

Here's an image to a cooling system for your reference. Each vehicle has it's own unique setup. The differences in some cases are slight and in some very big. You can see the placement of your ...
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5 votes
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How does clogging tailpipes result in carbon monoxide in the cabin?

One way I could explain it from that photo, is that there will not have been any snow under the car, so the exhaust fumes will have easily been able to exit from the tail pipe and spread under the car....
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  • 19.8k
5 votes

Water dripping on driver's foot. How to fix it?

The air con water outlet pipe might be clogged. Get it cleaned by a mechanic. Happened to me some time ago, cleaned the outlet and now everything is fine.
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  • 8,916
5 votes

Does putting down the visors help defogging the windshield?

I would assume the visors would help to create / trap a column of slightly warmer air at the top the of screen instead of is dissipating across the headliner and into the cabin of the car.
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5 votes
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Why does the radiator fan have to start when turning the A/C on?

In a nutshell: The radiator fan comes on so the A/C works at its highest efficiency. The A/C condenser (the part which sits in front of the coolant radiator) is a heat exchanger. If air isn't ...
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5 votes
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Is it bad to immediately crank the air conditioning all the way up when you start your car on a really hot day?

I live in a very hot climate. There is no issue in turning on a properly-functioning A/C to its maximum setting at startup. Turning the A/C on activates the refrigeration cycle, which at startup will ...
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  • 38.9k
5 votes

How do race drivers clear foggy windscreens?

Fogging happens when there's a temperature differential between one side of the glass and the other. Most racecars are open - they remove the windows to save weight too, so the temperature inside the ...
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4 votes
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Why might lower settings of a dashboard fan not work if the highest does?

Great post, it really helped me solve the same problem. I took some photos specific to the Nissan Note, I can send them if you want to expand the article. My problem turned out to be a failed solder ...
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4 votes
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How do I flush out bad smells in my air conditioning?

Bad AC odors are usually related to poor drainage of condensation, which allows mold to grow. There is a small drain hose which allows the condensation to drip out, but this can get clogged up or ...
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  • 1,536
4 votes

2006 Jeep Commander - heater is only blowing hot air

bad air duct door You have multiple air duct doors in your car. One of them will control the air from your heater. You may have situation where the servo motor is bad in a particular door. ...
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  • 32.7k
4 votes

What can I do to prevent my air conditioner from smelling moldy as the temperatures begin to rise?

One trick that has worked well for me in preventing the musty smell is to turn the A/C off but leave the blower on about a minute or so before reaching your destination (if you are going to be parked ...
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4 votes
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Why doesn't my A/C blower motor have speeds anymore?

Check the blower motor resistor. When it goes bad it defaults to high speed. The resistor is usually near the blower motor.
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4 votes
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Does outside temperature sensor affect the HVAC system?

No, the outside temperature sensor should not affect the HVAC. That sensor is only there to give you the outside temperature reading on your dash. Modern climate control systems use temperature sensor(...
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3 votes
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Why is there no vent option for combined defrost/face?

Yes, the option exists in some models. E.g. in my 2002 Opel Astra, I can enable/disable any of the air channels on climate control independently from others: Usually, there's one ventilation duct ...
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