91 Jeep Cherokee How to Pull Vacuum - JeepForum.com
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post #1 of 38 Old 05-17-2021, 04:32 PM Thread Starter
fhorta
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91 Jeep Cherokee How to Pull Vacuum

I have just replaced a bad condenser on jeep and in process now of pulling vacuum before refilling condenser oil and putting freon in.

I have manifold gauges blue hose on low side and red on high side with yellow to vacuum pump. I am getting no vacuum at all. Left overnight and nothing.

Oil level on vacuum pump is above the halfway full mark actually almost to full. It's brand new. If I take hoses out I feel suction on finger, just nothing if i connect. Also, nothing goes into low side and nothing comes out. I tried pumping compressed air into it but its like closed off. or something. It does have the retrofit R134 valves on low and high ports. Also no suction through low side neither. It's a 91 jeep so not sure if that's the years design how the compressor operates. I have seen videos mainly on 95's ac compressors how to charge, fill with oil and pull vacuum but this one seems to be different. Ideas. Suggestions please. Thanks

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post #2 of 38 Old 05-17-2021, 04:41 PM Thread Starter
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Also, not sure if this matters but i am using the manifold gauges that just snap on. There is no turning dial on them that some gauges have to depress the shrader valve in, but I do think they are depressing the shrader valves in compressor fittings.

I am able to pump air with air compressor using gauges through the red high side, but not low side. Another note is this car does not have the service ports on the suction and discharge hoses aka low and high so i am servicing straight from the compressor valves low and high sides. The vacuum pump I have is the Vivohome brand.

I have put freon in car before and as always, with car on and ac on full blast. Would car need to be on with ac on for ac clutch to engage and pull in through the low side or high side? I believe one is not supposed to charge freon on the high side.

Am I correct on trying to pull compressor oil through the high side? I am trying to add about 2.6 ounces of pag oil into compressor, but I want to vacuum first.

What I have seen on videos is with vacuum pump on, the blue side manifold gauge is closed off while the red one is open and the yellow one of course from manifold to vacuum pump. The guy then takes off the blue hose at the manifold gauge while leaving the end that attaches to the low side compressor attached and oil is sucked in via the blue side. When I do the same, there is no suction on the blue hose on the end that attaches to manifold gauge. But if i open the blue side valve and leave that end on manifold, and detach from compressor, I do feel the suction. Its like something is blocking that low side. But then again, the red side seems to be fine as it takes compressed air in. But after leaing that side open all night, no vacuum through there. Maybe both have to be open? Thanks again
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post #3 of 38 Old 05-17-2021, 05:08 PM
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Check those retro ports. It sounds as if they are not operating right. Some work with the old schreader valves still in place by depressing the pin. Others you must remove the old valves and the retro ports have their own valves. As for the vacuum pump the blue gauge hose goes on the low side port. Hand valve is open. The yellow fill/vacuum hose goes to the vacuum pump. Ignore the red hose/high side. Engine must be off. If there are no blockages then you should see vacuum reading on the gauge set. Even if the blue hose was not connected to anything the pump should pull vacuum in the gauge set. If you still get nothing try rigging up an adapter to the pump so you can use a common vacuum gauge to see if the pump is working right. As for oil I always remove a port and just pour the oil right in. Do it before vacuuming. The purpose of drawing a vacuum is to remove moisture. Water boils at 29" vacuum and you must pull at least that much so it will vaporize and be drawn out.

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post #4 of 38 Old 05-17-2021, 06:52 PM Thread Starter
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Yes old fittings are gone and new retro fits have own shrader valves. I will try to use blue hose instead of red to pull vacuum. As for oil i thought pulling vacuum was first before putting anything into it. I guess i was wrong thanks. But how do you just pour oil in? So just taking port off of low or high side from compressor and squeeze the oil in like with a plastic bottle and a very narrow tube or something? Just trying to picture it. I have a plastic bottle oiler that i use to oil bearings on house cooler. Something like that would work? Thanks again.
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post #5 of 38 Old 05-18-2021, 07:16 AM Thread Starter
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Also, correct me please, but i thought vacuum had to be pulled first before putting oil in. This would be because if compressor has oil still, then adding more oil would overfil ? Or would vacuuming not remove oil, just moisture? Thanks and sorry for confusion.
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post #6 of 38 Old 05-18-2021, 03:46 PM Thread Starter
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Ok. So it turns out this model's compressor has two on-off valves. One on top of compressor by high port for red, and the other, which I missed, right below for low side, blue. They are little shut off valves which you turn opposite way to open and close. Turn left , it closes, turn right it opens. This is to allow freon or other things to be put in compressor. That explains why nothing going in or out of that low blue port. I opened it now good.



They can be turned with 1/4 inch wrench.



Now i pulled vacuuum with both blue and red man gauges attached and open. . Blue side Got to about 31 green area. However, pressure begins increasing almost immediately after closing valves and turning off vacuum.



I pulled vacuum again and closed everything and pulled blue man gauge hose from compressor port and not losing vacuum now. Could it be the man gauge valve and or retro fit valve maybe pressing too far in? It holds vacuum if i pull the blue hose from compressor.
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post #7 of 38 Old 05-18-2021, 05:20 PM
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I'm glad you figured it out. After pulling vacuum for a good while you turn off the gauge set and vacuum pump. You watch to see if it holds. The FSM specs holding for like five minutes. I prefer a half hour. Then you KNOW there are no little leaks. No, oil goes in first. Otherwise you risk admitting atmospheric moisture. I use the low side service port to add oil by unscrewing the schraeder valve. . Yes, a small dispenser is best because the opening is tiny and you will spill plenty until you realize just how little you can add at a time. If there is no convenient spot then you can open a mechanical connection. Just use a new "O" ring lubed with oil when you close it back up. Of course the BEST time to add oil is when you replace the components. Each gets a specific amount and it is easy to add it right to the parts being replaced. Oil circulates in the system and pools at certain spots. That is why when you replace a component you are replacing the oil that would normally pool there. A very tiny leak that only lets freon out slowly will not carry oil out and you won't see any. A major leak WILL carry oil out and that is when you see a big splatch of oil on something. So you held vacuum, you have no leaks, now go ahead and add your oil. Since you just opened it up again, you must pull vacuum all over again. Do it for a half hour to an hour. Then when that is done- you can quickly re-charge the system. Only water boils at 29" vacuum. Oil does not. It stays behind. The 2000 XJ takes 1.25 pounds exactly of R-134. Yours is a retro-fit so there is a formula to convert the R-12 system capacity to R-134 capacity but I am unfamiliar with it. Perhaps someone else can chime in with that.

Mark in Queens- Home of Spiderman and the Ramones
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post #8 of 38 Old 05-18-2021, 05:35 PM Thread Starter
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Thank you. Now I'm a little lost on how much pag compressor oil to put in. The condenser had a pretty good size crack and compressed air was very apparent coming out, hence a big hole. Would it be safe to assume there is no oil present? In which o would add about 2.5 ounces.
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post #9 of 38 Old 05-18-2021, 09:01 PM Thread Starter
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I dont want to overfill. Also, on second inspection I m not entirely sure im losing vacuum through low side port. Right after reaching 30 on gauge with vacuum, I pull blue adapter, get rid of pressure in that hose and gauage reaches 0, I reattach adapter and gauge shoots back down to 30. If I leave adapter in it will lose vacuum. I vacuum ed to 30 right now and pulled adapter and released air in hose. If in the morning when I reattach adapter and shoots back down to 30 I would say losing vacuum through adapter\port. But If gauge shows something closer to 0, then not sure where would be losing vacuum. Is my thinking right? Thanks
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post #10 of 38 Old 05-18-2021, 09:12 PM
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I don't think the entire system oil would get out. Was there a lot accumulated around the break? Can you guess how much by the stains? Either way I would add what the amount is for the condenser, plus maybe an ounce or two if it looks like that much puked out. An ounce or two extra won't hurt the system, it will just pool in the usual spots.

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post #11 of 38 Old 05-18-2021, 09:16 PM
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Yes, you are on the right track. The gauge set fittings use "O" rings too. They can leak. If you leave it overnight and there is still 30" vacuum then you have a good tight system there.

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post #12 of 38 Old 05-19-2021, 08:51 AM Thread Starter
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Ok, so left it at 30 vacuum overnight isolated no hoses attached. This morning lost all vacuum. Now I'm not sure where leaking from. I done a compressed air test , sprayed hoses, fittings, attachments with soapy water but found no bubbles. Also, I dont lose compressed air pressure.

I have also sparayed with soapy water right after pulling vacuum but no bubbles. Could it be its leaking through port but so slow that not producing bubbles? I also tried closing those two valves mentioned but still lose vacuum. Thanks again.
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post #13 of 38 Old 05-20-2021, 01:53 PM
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There are three kinds of leaks, positive pressure only, vacuum only, and a combination of both. There can be any combination of these. Soapy water will only show a positive pressure leak. A vacuum leak will suck the soapy solution INTO the system. Not what you want. Also, compressed air has moisture so also not what you want in there. Vacuum down again. Then try adding a small amount of R-134a then look for leaks with the soapy water. About 10psi should be enough. Also, the FSM says the system need only hold 26" hg vacuum for five minutes. So overnight is not a valid test. I use a half hour for my own satisfaction, but five minutes is OK. Quite often, a vacuum leak will seal under pressure, so vacuum down then add some freon and see if it stays in there.

Mark in Queens- Home of Spiderman and the Ramones
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post #14 of 38 Old 05-20-2021, 03:44 PM Thread Starter
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Ok. Sounds good. Is it possible there is a ac compressor shaft seal leak? If so, would i be able to see that leak with freon or with dye? Or is there another way to check that seal? Thanks again!
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post #15 of 38 Old 05-20-2021, 05:54 PM
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Since the compressor is the only moving part in the system, it is generally the problem child. You would see a leak with dye and UV light but only if the leak was large enough to carry oil along with it. An electronic freon sniffer is a good tool but hard to use unless you can isolate the car from moving air. I knew a sharp AC tech that would place a problematic car in a closed part of the shop. Then the next morning he would literally sneak up on it without disturbing the air so he could test with the sniffer.

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