How cold should AC return line be?

Author: Mr. Casey Miller Sr.  |  Last update: Saturday, July 4, 2026

The cool/cold line is known as the suction line or ac return line. It conveys fluids, such as refrigerants, at temperatures of about 40°F [4.4°C]. The liquid line conveys warm/hot fluids at about 110°F [43.3°C]. Finally, the discharge line is typically very hot and operates at about 150°F [66°C].

What is the normal temperature for return air?

Well, the general consensus is somewhere between 14 to 20 degrees colder than the intake temperature. From my example, 55 to 61 degrees would be an acceptable range.

What temperature should the liquid line be on AC?

Also, note how much warmer the liquid line is than the outdoor temperature. It should be between 3°F and 20°F warmer than the outdoor temperature. If it is above or below that range, connect gauges.

Should an AC refrigerant line be cold?

The larger or low side line should be cold and usually sweating, the high side, or smaller line should be hot to the touch if the compressor is doing its job.

How cool should my house be if it's 100 outside?

When temperatures exceed 100 degrees Fahrenheit outside, setting your air conditioning (AC) to around 75-78 degrees Fahrenheit is generally considered efficient. Here are some reasons for this recommendation:

Learn about Cold Air Returns & Heat Runs - DIY

How cool should my house be if it's 110 outside in summer?

Just because the outdoor temperature is above 100, the Ideal temperature to set your AC unit to doesn't change — it's 78 degrees. Higher temperatures in the home are to be expected when the weather is hotter than usual, but your thermostat can still be set the same as if it were a lower temperature outside.

Should my AC keep up on a 100 degree day?

It's true that air conditioners do have limits when the outside temperature is extreme. This means that your air conditioner may be able to keep your home at 77 or 78 degrees when it is 104 degrees outside.

How cold should the AC return line be?

Ideally, there should be a temperature differential of around 14° to 20° Fahrenheit between the incoming air and the air being blown out by your air conditioner. This means that if the air entering the system is 75°F, the air coming out of the vent should be between 55°F and 61°F.

Why is my AC line not very cold?

The Copper Pipe (Suction Line) should be sweating and cold to the touch during a hot day. If it is not cold, your compressor could be off (bad capacitor/ hard start kit) or low on Refrigerant. Your Breaker is Tripped. Be Careful because this usually indicates a problem with the compressor or wiring.

What temperature should refrigerant line be?

The cool/cold line is known as the suction line or ac return line. It conveys fluids, such as refrigerants, at temperatures of about 40°F [4.4°C]. The liquid line conveys warm/hot fluids at about 110°F [43.3°C]. Finally, the discharge line is typically very hot and operates at about 150°F [66°C].

How cold should AC supply be?

If the AC system is operating correctly, then the air coming out of your vent should be about twenty degrees cooler than the regular temperature inside. So, if you're cooling it and the house is 80 degrees, then you would ideally want the air to be about 60 degrees. Have more air conditioner questions?

Why is my liquid line cold on my AC?

If the filter drier is restricted enough, it will feel cool or cold to the touch. This phenomenon happens from some of the liquid refrigerant experiencing a slight pressure drop and expanding into vapor as it travels through the filter drier.

Why is AC not blowing cold air?

First, check your filters and coils for dirt and debris that may be impeding airflow. Once you've cleaned the filters and coils, run the air conditioner with just the fan so that the ice accumulation can melt off. If the AC still doesn't blow cold air, it could be that refrigerant levels are too low.

What temp should condensing return be?

Condensing boiler systems need the return water temperature around 80°F or lower to achieve peak efficiencies. Elevation, fuel type, and water temperature rise also affect the boiler's ability to capture latent heat from its flue gases and reach optimal operation.

Why is my air return cold?

Dirty filters, leaky ducts, and poor insulation can cause cold return vents. Leaky ducts often cause cold air to blow even after cranking the heat up. 20-30% of air, especially hot air, is lost because of leaky ducts. Cracked, holey ductwork needs sealing or replacement.

Should AC refrigerant line be cold?

Go outside and look for an insulated copper pipe running from your outdoor AC unit to your home. There's refrigerant inside, and it should be really cold during the summer. When you touch the copper (some will be exposed between the insulation and the unit), it should feel cold.

Why is my AC not cooling below 75?

Your AC might be stuck at 75 due to various reasons like clogged filters, refrigerant leaks, or the wrong unit size. It's best to have a professional diagnose and fix the issue.

Should my outside AC unit be blowing cold air?

If your air conditioning unit is ac blowing cold air outside, it might mean there's a problem with cooling the air inside. This could be due to refrigerant leaks, frozen coils, electrical issues, or airflow problems. It's important to find out why to fix it and keep the cold air inside.

What temperature should AC return vents be?

While there isn't any perfect temperature you should set your HVAC system to, there is an ideal temperature difference between the supply and return air, which should be between 16 and 22 degrees Fahrenheit. This difference in temperature is the evaporator Delta T.

Do HVAC return lines need to be insulated?

Supply ducts in an unconditioned attic must have insulation equal to or greater than R-6. All other supply ducts and all return ducts in unconditioned spaces must have insulation equal to or greater than R-6.

Which AC line should be cold in summer?

The suction line will feel cold to the touch because it carries cooled refrigerant that leaves the condenser. This line is the one to insulate.

How cool should my house be if it's 90 outside?

What should my AC be set at if it's 90 degrees outside? If the outdoor temperature is 90 degrees, it's recommended to set your thermostat between 75-78 degrees.

Is it OK for home AC to run all day?

The constant running of your AC unit will reduce pressure in the evaporator, or cooling coil until it freezes over, according to Cool Today. This is why in some cases, this constant running can be dangerous.

Is 72 degrees good for AC?

Setting your air conditioning to 72°F is generally considered a comfortable indoor temperature for many people. It strikes a good balance between comfort and energy efficiency, making it a popular choice for residential settings.

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