A/C compressor oil and refrigerant

[Archieb89]

My liquid line to evap inlet was not holding and pressure so I'm re-doing most of my ac system. Everything but the compressor and condenser. The compressor is a replacement that the PO put in awhile back and it's a 4 seasons so I dont have high hopes for it but It looks like it's in good shape and I can here the internals working if I move the pulley by hand. I also applied power to the clutch with my power probe and it engages fine. The condenser is also the older tube and fin style that also looks to be in good shape so I'm just going to flush it for now. My question is how much and what kind of oil for this system, how much should bee added to each component? And how much r134a? I've read about 2 ounce per component and 3 in the compressor adding to about 9 ounces of pag 46, and 36oz of 134a. Is that correct for this system?
91 f350 with 7.3 idi

Also I took the compressor out to drain any oil in it so I can fill to the correct amount. After I get everything together I'm going to pull vacuum on the system and make sure it's not leaking before I fill it.

 

[Nero]

If I remember right I used 8-10 ouncses of pag150 and the total charge was 2.7lbs

 

[Archieb89]

If I remember right I used 8-10 ouncses of pag150 and the total charge was 2.7lbs

Do you recommend a variable orifice tube? I've heard mixed things about them. Like them failing often so I just got a motorcraft red fot. Just wondering if it'd he worth trying one. I live in upstate sc and it's hot and humid most the year so the colder the better

 

[franklin2]

Ford usually uses the PAG oil with r134a. But your truck was originally filled with r12 and used mineral oil.

Someone converted it. If they converted it and did not flush it and left the mineral oil in place, they used Ester oil during the conversion, it plays nice with the mineral oil left in the system.

During the conversion if they flushed it, then they could use Ester oil or Pag oil.

If you flush it and clean it out good, you can use whatever oil you choose, most people use Pag.

When filling, put two 12 ounce cans in it, should be enough.

I do not use any different type oifice tubes. But I do usually adjust the low pressure switch some.

 

[Nero]

A variable orifice is a lot more efficient than a fixed orifice tube, but im not sure if they made them as an option for these years. I switched my fixed one for a red one years ago, works just fine still.

 

[Archieb89]

They do have one from a couple manufacturers that I've seen but I'll just stick with the red for now. If it's not cold enough maybe I'll switch over later on

 

[Archieb89]

Ford usually uses the PAG oil with r134a. But your truck was originally filled with r12 and used mineral oil.

Someone converted it. If they converted it and did not flush it and left the mineral oil in place, they used Ester oil during the conversion, it plays nice with the mineral oil left in the system.

During the conversion if they flushed it, then they could use Ester oil or Pag oil.

If you flush it and clean it out good, you can use whatever oil you choose, most people use Pag.

When filling, put two 12 ounce cans in it, should be enough.

I do not use any different type oifice tubes. But I do usually adjust the low pressure switch some.

How do you go about adjusting the low pressure switch?

 

[franklin2]

You will want to adjust it if the compressor seems to prematurely cut off and then cut back on. If you have plenty of refrigerant in it, and it's cooling good on a hot day, and all of a sudden the compressor kicks off, then kicks back on, you can unplug the wiring plug to the low pressure switch. In between the terminals of the switch should be a small flat head screw. Turn it a little bit, then plug the wiring back in and try it. If you went the wrong way it will be worse, cutting off even more than it should. If you went the right way, it should cut off less.

On a cool morning, when you have the controls on max and are recirculating air in the cab, the compressor cycling is normal. That is how the system controls the cooling. If it's a hot summer day, and you are bringing in outside air, it should not cycle if you have enough refrigerant in it.

If you turn the low pressure switch too far, it cools great, but it turns the inside evap coil in the firewall to a huge block of ice (been there, done that). The reason I could tell that was happening, on a really hot day I would use the A/C, working great. But I would park the truck and go inside the store, when I came back out, I had this huge water puddle under my truck. Not just a small normal puddle, it was running out from under the truck and running across the parking lot under other vehicles.

 

[franklin2]

Another thing I have had happen quit frequently on older vehicles, the compressor clutch gap will end up getting too wide. That will also make the system cool intermittently. It should not be over .030 or so. On my truck I got everything working great in the driveway, but as I went down the road it would quit cooling. And then it would randomly start cooling again and then quit cooling again.

Took awhile to figure that one out, but found out the gap was over .050 wide. You can go to the store and rent a compressor clutch puller. Pull the clutch and you will see some small washers, they call these shims. I had two. I took one out, and the gap ended up being too small, and the compressor clutch would drag a little bit sometimes and try to turn the compressor a little bit when the clutch was not on. But I figured it would wear in and it did.

 

[Archieb89]

Another problem. The evaporator i ordered for this vehicle specifically is wrong. The brakes that stick of the evap core outside the hvac box is too short and won't let the box seal... anyone know a correct part #? I ordered this one from rock auto. Haven't had any problems before but this is p****** me off. I just wasted a whole day and $80 on that thing. It looks identical at first glance but then you see that bracket is about a 1/4" too short.

 

[franklin2]

I would clean the old one up and use it. Unless they leak, they rarely have a problem since they are right after the orifice with the screen in it. The one worth replacing is the condensor in front of the radiator. Anything that goes wrong with the compressor, ends up inside the condensor.

 

[Nero]

I agree with that. I'm running my original evap, but I'm running a condenser from a 1997 f150 and a new dryer.

 

[Archieb89]

I would. Only problem is the original quick disconnect fitting is all messed up and I'm pretty sure thats where it was leaking from. Not really sure what happened to it but looks like someone tried to take the hose off without the correct tool

 

[Nero]

Try to smooth it out as best you can, if I remember right theres two o rings on the other end for sealing. Did you replace those?

 

[Archieb89]

Yeah I've got all new hoses and o rings. I'll give it a try.