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I just noticed whenI trun on my fan on full and my air controls on, this wire that goes to the compressor that is to supply positive 12v power is getting nothing? does the expansion valve turn it on or should it always be on?

OK here is what I am dealing with and maybe someone can give some insight on what to look for or what to do with this air conditioner system

Older 1985 International Truck, was a r-12 system that someone supposedly removed the older oil and changed over to newer R-134a

so here is what I did, when I started this the truck air conditioner compressor would cycle but no cold air, at one time there was cold air but that was last year.

Now to today, I removed the old rusted out receiver /dryer and replaced it with a new one and replaced 1 new line that was bad and rusted. Before installing the new line and receiver/ dryer I removed the lines off the compressor and flushed the condenser and and the evaporator with a flushing agent for air conditioner systems, the blew all lines out with air until nothing was coming out . installed the new line, receiver/dryer, new o rings, and re-installed the lines on the air conditioner pump with new o rings. then vacuumed the entire system, low and high side for 45 minutes. Watched it for 5 minutes after to insure it maintained negative pressure before starting to load it.

I started with a 6 oz can of ester oil and r-134a and noticed the pressure with the unit running shot right up low side 35 psi ,high side stayed low , pump would not engage. Added another 6 oz can of the ester oil with 134a and unit running but pump still would not engage, for some reason I was not getting power to the compressor unit? so I added 12 volt power to engage the pump manually while running to see if the unit would load any r-134a, the low side seemed as if it did not want to take the 134a, and noticed the pressure on the low side going to 80 lbs while the high side stayed all the way down to about 20 lbs?

What would stop the power from getting to the compressor ? why is the pressure not correct? what turns the pump power on and off? I didn't see a expansion valve or orifice tube where is that hiding and could these cause the problems? I dont knwo why it would cycle before I did this stuff? and ideas I m showing some pictures , may be I can get a little help, thanks

the previous owner told me he had the pump off few years ago and changed the oil so I was wondering cant I just change the receiver/dryer then vacuum it and reload the system with 6-8 ounces of ester /134a in the can right into the low side port then follow with r134a ?

PAG oil is 100% synthetic in manufacture. Ester oil is a modified blend of organic oils. The viscosity of the oils is rated in centistrokes at 70 degrees (F). There is not much of a way to tell what the high side or red gauge will read. This depends on ambient temperare, refrigerant charge in the system, cooling fan efficiency, condensor and evaporator cleanliness, airflow through the coils, etc.

R-134 will work with either Ester oil, or PAG oil. Should you use PAG oil, the sealing "O" rings in the system must be changed as the oil will eat them on short order. If you use ester oil, I'd still replace them as they are aged and probably leak. The accumulator/dehydrator, or receiver/drier must also be changed if the system is converted, or has been left idle with no charge in it. They are not to be reused.

Being an older unit I'm making the assumption the compressor is a York style two cyliinder piston compressor. If so they are the best, (my opinion). You must however remove the compressor from the engine, (no matter what type) pull out the drain/fill plug and drain the oil out of it into a calibrated beaker for measurement. Compare this to specification(s) for capacity. Refill the compressor with PAG, or ester oil in the amount removed. Do not add more unless the system suffered catastrophic failure such as a ruptured hose etc. When the compressor is refilled, set on the bench and turn the clutch and compressor 10 full revolutions clockwise to distribute the oil onto the parts. Tape or cover the openings to not allow dirt to enter the crankcase.

Remove and throw away the accumulator or receiver. These parts are not to be reused. If you don't know the difference between the two, a receiver/dryer is in the high side on the outlet path of the condensor coil, and accumulator is on the outlet side of the evaporator inside the dashboard. Most receiver/dryers have a sight glass in the top also, Accumulators do not. Remove, and/or check the expansion device for cleanliness. If an orifice tube, in the trash it goes. A thermostatic expansion valve unless suspect can be reused.

Before reconnecting anything ascertain how much oil the system requires. This can roughly be figured by following this formula:

Oil amount (oz.) = [(Refrigerant charge in oz. x 0.06) + 2.2] ÷ 0.9. I've used this for years myself. You have to have enough oil in the system to circulate with the refrigerant but too much and you will slug the valves out of it. Too much oil also acts as an insulator reducing cooling effectiveness. Citing that you have already filled the compressor, if the system uses a receiver/dryer, dump one ounce into this new part, and the balance into the evaporator core inlet. If an accumulator system, do not dump oil into the evaporator but dump the oil into the accumulator. Reconnect everything using all new polyurethane "O" rings, and seals.

Once everything is reconnected, ensure the condensor core is clean with both an air gun, and garden hose. This is above important and one of the most widely skipped steps in maintaining an automobile. The cleaner the better here. Pull the a/c system into a 29.75 inches of vacume for at least 45 minutes. Shut the vacume pump off, close your manifold valves and ensure the system hold this vacume for at least five minutes. If it holds, administer refrigerant into the system high side as a liquid, but don't exceed one pound. Stop the charging, allow the liquid refrigerant to "boil off" into a gas. you will see this as the low side pressure gauge ascends to about 50 psi. Wait a couple of minutes, Start the engine and run at 1500 rpm with the doors open, blower on high speed and start to administer refrigerant into the low side of the system as a vapor. The compressor may cycle off and on until the system charge elevates enough to satisfy the low pressure cutout switch, or you can bypass this switch if you know it works. Continue to charge until your low pressure gauge is indicating about 35 degrees denoted on the inner temperaure scale toward the center of the gauge. High side pressure can be as high as 350psi but if that high the condensor coil is partially plugged.

This is very generic in nature but will get you in the ballpark.

Rob

very informative,, thank you!

I have a older truck, not a mack but a international that has the old R-12 air conditioner system on it, I know how to do the changer over basically but I dont understand 3 things if someone can help?

1) When I add the first can of pag oil to the system before I add cans of r-134a what viscosity should I use I seen the local parts stores sells Low (46), medium (100) and high (150) viscosity cans of pag oil ?

2) What is the difference between pag oil and ester oil in the larger can?

3) What should my gauges read on the low and high side ....should be reading when I load it so I dont under load it or overload it?

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check the line going into commpressor, it should be sweating up to the nut, but not on the nut.

if the nut is sweating it has to much......

Ok thanks I will check it out..

At high idle (1000 rpm's) and the fan engaged, the high side should be between 250 and 450. The low side should be between 30 and 40.

wow 250 - 450 ? that's high I never would of thought of that..

Any idea what would make the clutch on the air conditioner compressor to stay engaged

Have a mack rd model and trying to find out what the gauges should read on the air conditioner LOW pressure side and HIGH pressure side ?

want to make sure its not over charged, because My clutch unit is not kicking off automatically..

temp in my area in the summer is 70-90 degrees

its blowing very cold air..

any help would be great

Have a older RD model dump mack and noticed every time it rains I get water on the floor under the dash mostly on the passenger side, where is this coming from?

the vent in the front center is closed..

anyone? driving me crazy!