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Compensating for excess gas and oil left in Manifold/hoses when charging?

Z2TT on Mon November 08, 2010 1:00 AM User is offline

I'm wondering about charging procedures, is when your charging by weight with a scale on the cylinder.... you know the amount that has left your cylinder as the scale measures while charging, but I read that 100 grams of refrigerant will remain
on a 2 meter set of hoses, so that would be about 150 grams on a 3 meter set (high, low, common each 1m long?). And this gas will just remain in the hoses and not get in the system. So is there anyway of getting the correct charge when going by weight.
100 - 150 grams could be a 10-15% Undercharge as it stays in your manifold. I've never read a way to get past that when charging by weight.

Could some of these suggestions work or not... what do you guys recon? If not what is the best way to get most of the gas left in your manifold back into the system.

1. Let your scale meter in 10-15% more gas than specified charge for car to compensate for the amount that sits in your manifold and hoses and doesn't enter the system?, so in turn you get the specified charge in the actual system.

2. Give 5-10 minutes of gauges sitting connected when you turn the car off so when the pressures lower, more gas naturally is drawn into the system from the manifold as pressures lower in the system?

3. Once your complete charging and system still running, and if your hoses have valves on the ends, shut the valve off on the high side hose, remove high side charge hose from the fitting on the car, and let the remaining gas in your manifold
get sucked in through the low side as pressures are lower there and more gas would naturally want to enter?

Also some oil from the system will also be left in the manifold, what is the best way to get that to drain back into the system?


mk378 on Mon November 08, 2010 9:15 AM User is offline

It's really a tiny amount, less than an ounce. Same thing with the oil, not enough to worry about. #1 will leave you overcharged. If you're going to add more to compensate for losses during charging, I'd suggest 2 oz max-- not a percentage of the rated charge. #2 may or may not work. #3 is what I'd do. It does not work with cheap R-12 manifolds that don't have self-closing hose couplers though.

The main thing is not to leave liquid refrigerant in the red manifold hose (it will naturally accumulate when running the system with hoses attached, as the manifold hose is the coldest part on the high side). Liquid is of course much denser than gas, and also storing the manifold with liquid trapped in it can cause it to overpressure.

newton5 on Tue November 09, 2010 12:53 PM User is offlineView users profile

I don't recall where I was taught to do this, but when I'm finished weighing in the charge and verifying the system pressures I:
-Close off the center charging hose from the refrigerant supply.
-Close the valve on the high side coupler.
-Open both the High and Low side valves on the manifold.
-Raise the engine speed as necessary to draw the remaining refrigerant out of the manifold set into the low side of the system.
-Close the valve on the low side coupler.

This leaves very little refrigerant in the manifold set. Usually much than an ounce.

NickD on Sat November 13, 2010 8:53 AM User is offline

Let's first address the oil problem, makes a mess out of your hoses, get an oil injector, and with the injector, assured most of the oil gets in your system.

Typical hose is 3' long 1/8" diameter, yellow and blue add up to 6' or about 0.9 cubic inches. at a charging pressure of 30 psi gas less than a cubic inch of expanded gas, not liquid will be left in the hoses, have more important things to be concerned about. That works out to losing 0.0015 ounces of refrigerant.

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