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Old 07-21-2011, 12:31 AM
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Location: Florida USA
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Vehicle: 1995 Dodge Ram B2500 Van
Trim Level: SLT - 2500
Color: Deep Molten Pearl Coat, Silver, Grey
Engine: 1994-2001 318ci (5.2L) Magnum V8 220hp
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Originally Posted by sonocativo View Post
Oh, and as you say the low/high side... I add the 134a at the port in front by the radiator, it fills and gets colder as well as empty the can , The cans come with the hose/fitting and it fits on with no leaks or anything so I assume its the low
I'm guessing from you uncertainly that you have really no idea what you're doing. So I am going to help you on this, if I lived near or vice versa I would do it for 20 bucks. But heres the brake down.

You have two valves on is high side (largest valve) and one is a low side (smallest valve). Obviously the low side is lower pressure typically between 30-50 PSI and the high side is high pressure anywhere from 125-300 PSI.

When low side pressure increases so does the high pressure, however it varies based on temperature variables.

You have a evaporator and a condenser. The condenser sits outside the vehicle probably infront of the radiator and the evaporator sits some place inside the dash. The evaporator is gets cold the condenser gets hot, what the condenser does is to boil down the liquid refrigerant into a gas again, 134a boils at around -26 C.

The filter drier is basically a can with a dessicant that is used to remove moister from the system and it also stores liquid refrigerant incases of overfill and loss. It is wise to replace this part after so many years, thats why I say every 6 year overhaul the whole A/C system.

Then you have expansion valves, these control the flow of refrigerant, these typically don't have to be replaced normally the thermostatic ones do though. BTW Their are 3 types of expansion valves.

The system is sealed with O-rings, when two fittings connect their is an oring to seal it, when you connect a valve to a line o-ring. O-Rings to be replaced every 6 years blah blah blah.

Ok then you have you compressor which I'm sure you know about. And lastly you have your refrigerant oil and refrigerant.
Normally you don't have to add oil to the system usually the compressor is shipped with a fixed displacement of oil however sometimes you do have to add oil when you replace alot of parts that had stored oil or when you have an additional A/C system like in the vans, etc... The oil is basically used to lube the compressor and to keep the system from rusting from the inside out.

The refrigerant well nothing to say their, you can use many things as refrigerant, propane, butane, etc... But stick with 134a.

Now to move on to the tools of this flimsy trade.
You have your manifold, vacuum pump, and thermometer.

Ok their are two types of manifolds R12 and R134A. But we will only talk about 134a.

To start off the manifold has two hand valves a low side and high side, it has two gauges high side low side, and has two quick connect couplers high side and low side and on the couplers you will find little valves turning it clockwise opens it and counter clockwise closes it.
Then you have your hoses, you have a red one which is high side and blue one which is low side and then the yellow hose known as the service port. The yellow hose will connect to things like vacuum pumps, refrigerant cap taps, and of course the manifold it self to make a sealed loop.

Ok to start off, if the system is in need of repair make the repairs then fallow.

Connect the low side coupler to the low side valve on the vehicles ac system, then connect the high side coupler to the high side valve. Be sure the valves on the manifold are closed.

Now open the valves on the couplers by turning clockwise. Ok be now connect the yellow service hose to the vacuum pump.

Turn the pump on, then open the low side valve on the manifold then open the high side valve on the manifold, open these valves 100%.

Now let the vacuum pull in 28-30 in Hg for about 1 hour, this vacuum will eventually cause what ever moister or water in the system to boil to a vapor and will be sucked out.

Ok now close the high and low side valves on the manifold then turn the pump off and disconnect the hose from the pump. Now to check for leaks look at the manifold's low pressure gauge and read the vacuum, then come back 30 minutes and observe if the vacuum has decreased, if it has then their is a leak if not proceed.

Now we will skip adding oil, now to add refrigerant using those little 12 Oz cans. You will need a can tap so we will say you have one already.


Take the can tap and turn the valve counter clockwise and then screw the tap onto the can, then connect the yellow hose to the tap. Now turn the valve on the tap clock wise, this will open the can. Now turn the valve counter clockwise to open the valve, then at the manifold side just loosen the yellow hose and allow some of the refrigerant to escape this will purge any air from the service hose, air in the system will shorten the life of the system and will also contaminate refrigerant thus making it useless meaning that the system won't cool as effectively as it could.

Ok once you let some of the air out (about 4 seconds) tighten that hose back up, now you can begin to add refrigerant to start off you can put the key in the ignition and start the car. Then with the car running turn the A/C on the maximum settings then go back to the manifold and turn the blue (low side valve) on slowly until it's opened 100%, you will want to shake the can left to right rapidly, make sure the can is up right because you don't want liquid refrigerant on the low side, the low side cannot handle liquid refrigerant very well. The first can will empty out quickly and the can will get very cold so wear gloves. It will only take about 7 minutes to empty the 12 oz can, during the first can the compressor will cycle on and off until their is enough refrigerant in the system to keep the compressor from burning up. Ok once the can is empty you will shut off the low side valve on the manifold. Then loosen the yellow hose at the manifold a little to allow the residual pressure in the can to release. Once thats release you can remove the can then install the next one.

Be sure to fallow the same purge procedure for each can.

When you remove the couplers from the valves be sure you close the valves on the couplers first then remove the couplers, you can allow what ever gas is left in the manifold to release by unscrewing the yellow hose and opening both high and low valves on the manifold. Don't let the refrigerant or oil get on you.

You can get a manifold at a harbor freight for 40 bucks or you can go to autozone get one for about 50 bucks or rent one for 90 bucks (it's refundable)

The can tap runs you about 7 bucks. The refrigerant like I said 8 bucks a can at big lots

You can also get a vacuum pump at harbor freight for 100 bucks.

If your wondering about the high side valve why is it even their, well their is many ways to add refrigerant, the slow way is gas and the fast way is liquid, Liquid goes in the high side and gas in the low side, but don't try the fast way because it's alot more complicated then you think. It's mainly used when mass producing A/C systems, so basically when it's made.

Things you might get worried about, when adding refrigerant, at probably either the first or second can the manifold might get very very cold and condensate. This is normal.

Any questions ask me no problem
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