Refrigerant volume

Turbofiat on Tue July 12, 2011 11:12 AM

I got to thinking about something. How to know if a custom system is fully charged.

Shouldn't the hose coming out of the compressor, the condensor, the dryer and the hose going to the exapansion valve be full of liquid? Or at least the condensor be full of liquid refrigerant.

Then the evaporator should be empty (or gas) as well as the hose going to the compressor?

If so I did some math to see how close I was at charging my custom built system.

I don't know if I did the math correctly but here goes.

If the condensor is 12"X20" and assuming the tube size is roughly .5" in diameter that would give me an area of .196"

So 12"X20"X1.96" should equal 47 in3.

I added two 12 ounce cans of R134a which gives me a volume of 43 in3.

This is not taking into account the dryer or the hoses between the compressor, condensor and expansion valve.

So does that sound correct?

I have done some other tests:

Assuming the ambient temperature is around 90F:

The fitting coming off the bottom of the condensor is 155F. This is with the radiator fan running. Temperature coming out of the vents is 50F. While driving down the road, the temperature will drop an additional 5 degrees (45F). This is an under the dash unit so air is being recirculated.

I was using a heat pen to test the temperature of the fitting leaving the condensor so this test would be impossible to do while driving. To see if moving cools the refrigerant down even more.

On another note, one morning it was 68F and I tested the air coming out of the vents. This time the air temperature coming out of the vents was 40F.

I'm just trying to figure out the limitations of this system. This is a Fiat convertible and is poorly insulated so getting the temperature down as low as I can without freezing the condensor would be a plus.

I've insulated the inside of the top with bubble foam insulation because I aimed a heat pen at the inside of the roof one day at 88F and the top measured 140F!

As of now the system keeps me fairly comfortable when it's in the mid 90s. I'm not sweating but it won't cause me to get Bell Palsy like my father came down with after a week at the beach with the A/C blowing directly at his face either.

mk378 on Tue July 12, 2011 11:28 AM

The condenser can't be full of liquid. It needs to contain gas that is condensing and the resulting liquid draining out quickly. Once it's condensed, liquid is just in the way of further condensation. Likewise, the evaporator should be mostly full of liquid.

If you go to Dupont's site, there are pdfs with tables of the density of R-134a under various conditions.

Automotive Air Conditioning Information Forum (Archives)

Turbofiat on Tue July 12, 2011 11:12 AM

mk378 on Tue July 12, 2011 11:28 AM