# Freon compression and air conditioners and refrigerators

**URL:** <https://boards.straightdope.com/t/freon-compression-and-air-conditioners-and-refrigerators/74691>\
**Category:** Factual Questions\
**Created:** [August 2, 2001, 8:46pm UTC](https://boards.straightdope.com/t/freon-compression-and-air-conditioners-and-refrigerators/74691 "2001-08-02T20:46:42Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\
**Post date:** [August 2, 2001, 8:46pm UTC](https://boards.straightdope.com/t/freon-compression-and-air-conditioners-and-refrigerators/74691/1 "2001-08-02T20:46:42Z")

</div>

I was thinking the other day about how air conditioners and regrigerators work. I get that the compressor pump compresses the freon, which gets cold, absorbs heat, expands, and radiates the heat on the other side via the radiator.

What I don’t get is _why_ something would get cold when you compress it. It seems to me that compressing something would be _adding_ energy to it, just like sticking it above a fire or zapping it with electricity. So why does it get cold when you’re adding energy?

---

<div class="post-metadata">

**Author:** ![Running\_with\_Scissors](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Running\_with\_Scissors](https://boards.straightdope.com/u/Running_with_Scissors)\
**Post date:** [August 2, 2001, 9:02pm UTC](https://boards.straightdope.com/t/freon-compression-and-air-conditioners-and-refrigerators/74691/2 "2001-08-02T21:02:23Z")

</div>

Actually, you’ve got it backwards - it’s the expansion that cools the fluid; compression heats it. Think of how hot an air compressor gets when it’s running. Same thing here.

As usual, [HowStuffWorks](http://www.howstuffworks.com/ac.htm) has a great answer.

---

<div class="post-metadata">

**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\
**Post date:** [August 2, 2001, 9:09pm UTC](https://boards.straightdope.com/t/freon-compression-and-air-conditioners-and-refrigerators/74691/3 "2001-08-02T21:09:25Z")

</div>

Doh! I feel dumb now. 🙂

---

<div class="post-metadata">

**Author:** ![cornflakes](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@cornflakes](https://boards.straightdope.com/u/cornflakes)\
**Post date:** [August 2, 2001, 9:09pm UTC](https://boards.straightdope.com/t/freon-compression-and-air-conditioners-and-refrigerators/74691/4 "2001-08-02T21:09:40Z")

</div>

(Can I post this before someone links to How Stuff Works? Probably not…)

It doesn’t get cold when you’re adding energy, the refrigerant gets cold when it is allowed to expand.

Air conditioners work roughly along the lines of the ideal gas law:

PV=nRT, where:[ul]P=pressure  
V=volume  
n=number of gas molecules present  
R=a constant  
T=temperature (degrees Kelvin for the Ideal Gas Law, but I doubt things are this linear here.)[/ul]

The air conditioner has a compressor that pushes the refigerant through a closed loop with a restriction in it. Upstream of the restriction, the refrigerant is compressed, which heats it. As it goes through this area, it passes through a radiator (the condensor), where it dissipates heat and cools into a liquid. It then goes through the restrictor. Because of the reduced pressure on the downstream side, the refrigerant cools. It then passes through another radiator (the evaporator) where it absorbs heat and evaporates into a gas. From here, it goes on to the compressor, then back to the condensor.

---

<div class="post-metadata">

**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\
**Post date:** [August 2, 2001, 9:15pm UTC](https://boards.straightdope.com/t/freon-compression-and-air-conditioners-and-refrigerators/74691/5 "2001-08-02T21:15:19Z")

</div>

by the time I got to this it was already answered.