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Servicing after evac question

Skoobahead on Fri April 23, 2010 10:19 AM User is offline

Year: 1999
Make: Nissan
Model: Maxima
Engine Size: 3.0
Refrigerant Type: 134a

just replaced condenser. After I evac the system will I need to jumper the pressure switch to get compressor to engage when servicing? If so how long do I jumper?

mk378 on Fri April 23, 2010 11:17 AM User is offline

No you will not. Charge as liquid into the high side with the engine off until it won't take any more. That will build enough pressure to close the switch. Then start the engine and complete the charge as gas through the low side. To charge as liquid, have the container of refrigerant (can or 30 lb tank) upside down with the valve at the bottom. Remember never open the high side manifold valve with the compressor running.

Edited: Fri April 23, 2010 at 11:18 AM by mk378

Skoobahead on Fri April 23, 2010 12:24 PM User is offline

Filling high side with fluid is the only way to do this? Never heard of it done this way.
Just dont want to mess something up.


Cussboy on Fri April 23, 2010 10:52 PM User is offline

Right or wrong, here's what I do.

Connect service gauge set. Pull a vacuum at least half an hour.

Check for vacuum leak for about 45 minutes.

If vacuum is OK, connect can and allow the system vacuum to pull in refrigerant, can warm the can in warm (not hot) water, OK to shake can as well and let heat from hands warm the refrigerant can; agree that it would be OK to add as a liquid as well.

Turn on engine, turn on AC, compressor should engage on its own. Add remaining refrigerant as a gas until the correct toal weight of refrigerant is added. Turn off engine, disconnect gauges, replace the caps.

I assume that all hoses are bled free of air during this.

NickD on Sat April 24, 2010 6:14 AM User is offline

The trick is to connect your blue hose to your vacuum pump, using old R-12 fitting and a low side R-134a port, can make an adapter to do this. Is such an adapter available?

With the yellow hose connected to your refrigerant source, its valve closed, and red hose to high side, switch on the pump, open both low and high side valves on your manifold gauge and let the pump run. This draws a vacuum not only in the system, but clear up to the refrigerant source valve. Close off the low side to the pump, then open the refrigerant source valve, this provides a vacuumed path directly to the high side port so no air can get into the system. If using a can that only permits a maximum of 14 ounces, kind of a pain in the butt as you have to purge for each can, what a waste. But as long as that valve can is open, you can heat that can as hot as you want to, I use a heat gun.

You want the system temperature to be cool and the can to be red hot, this is what gets all the refrigerant out of the can, well most of it. But that can will explode if the valve is closed, this is pure logic, the pressure in the can will never be greater than the system and your high side gauge tells you exactly what that is. That is with the valve open. You can close off your high side valve even with a hot can, not much left in it to do any harm, but releasing the yellow hose immediately afterwards releases any remaining pressure.

After the initial charge, can hook up your gauges normally to finish it off, at this time, your system has positive pressure so refrigerant will leak out rather than air leak in. Always critical when even popping off a quick connector in a vacuumed system, it sucks air in like crazy. Four valve manifold gauge is far better for this so you don't have to switch hoses. As is a tank so you don't have to switch cans. A charging station is even better.

Whichever you use, have to be awake and men tend to have one track brains. Took me awhile to train my wife and daughter that when the damn telephone rings, its not the end of the world, some damn telemarketer anyway. Never understood why every one jumps when the phone rings, but got them trained well now, if important, they will leave a message, but that is extremely seldom. And not when I am charging a system.

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