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Old 09-19-2020, 02:13 PM   #1
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Any A/C experts on here?

Iím a die hard DIY guy... if it involves buying a new tool, Iím there...

My RV ac isnít working. Bought the amazon gauges and vacuum pump, which seem awesome...

I thought the system might be empty, as one of the line compression fittings has a crack in it...

Compressor cycles but wonít stay on...

Put on the gauges have 40 psi of r134a...

So, itís low. Running the ac drops the low side to 0-10 psi, high side to 50... which is low.

Peak pressure is supposed to be ambient tempx2 plus 50 degrees...

Seen lots of videos on YouTube, adding the r134 seems really easy. If the systems empty, you draw a vacuum first. But mine ainít empty...itís low. So I just add r134a on the low side until I hit the pressures I need...

Right? Some articles said to pull a vacuum... but how? You would just be sucking out the existing R134a?
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Old 09-19-2020, 03:27 PM   #2
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Unless someone closed it up a below zero temps and it now is extremely hot and the air expanded. It shouldn't have pressurized itself. So there shouldn't be any air/moisture in system, unless someone had it open and didn't vacuum it down ????. I am assuming its chassis AC . Did you get the digital gages with temperature calculations per pressure differential ? Is this a DP or gas chassis. There is a chart that will get you near perfect just by pressure for DP system. Can you find a weight of R134A on a plate or sticker. Your going to need a minimum of 40psi if above 70F on the low side for now. DIY best to shoot from hip charge at 80f-90f .Without any other info I would start there rpms should be 1000-1200 with good fan flow over condenser. Keep track of cans/weight used for now to get you to 40psi.
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Old 09-19-2020, 03:44 PM   #3
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You apparently have a leak and that is why it low. It would be a bad idea to attempt pulling a vacuum without repairing the leak first. Yes you can add refrigerant to top it off but it will leak down again if the leak isn't found and repaired.
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Old 09-19-2020, 03:59 PM   #4
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Here is chart for DP system shared before.Click image for larger version

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Old 09-19-2020, 04:00 PM   #5
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If it were me, I’d put a can of 134a with dye in it then run it for a while and look for the leak with a black light.

Once you find the leak you can either take it to a shop with a refrigerant recovery machine and have them empty it out, or just vent it to the atmosphere. Option 2 isn’t generally well liked by the tree huggers.

Once it’s depressirized, fix the leak and other potential leaks. I’d replace the dryer and txp valve while I was in there. Then you can pressure it with nitrogen to look for new leaks. Once you are sure the leaks are gone, vent the nitrogen out and put it on the vacuum pump for a hour or two. This will remove any water. Then add oil (whatever is recommended for your system) and refrigerant

There should be temperatures on the gages. These are your pressure targets at evaporator and condenser. Creep up on them be patient.
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Old 09-19-2020, 04:09 PM   #6
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Thanks guys... diesel pusher cat 3126...Chassis ac...

From what I gather this thing hasn’t had r134a added in 10 years... prior owner said he always just used the house ac...RV is new to me...

If all the Freon were gone, I would be vacuuming and looking for leaks...

The chart with the pressures isn’t readable? It’s 70 degrees out here, so does peak pressure of 180-190 sound about right?

I thought you set it by high side pressure, not low side?

I know it likely has a tiny leak, which eventually I need to get to...

Right now I have nothing to lose to just add r134a... worst case scenario I’m out $20...


Edit... figured out how to open the chart... thanks!
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Old 09-19-2020, 04:19 PM   #7
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Common places for leaks are the compressor shaft seal, the o-rings on the hose to compressor fittings, o-rings on the expansion valve, and the charging ports.

One of those cheap black light flashlights will tell you if you have a leak in about 10 minutes.

Just adding refrigerant for the time being is fine too. Eventually it will get bad enough that you will want to fix it
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Old 09-19-2020, 04:40 PM   #8
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I applaud you on your commitment to DIY--but a little knowledge can be a dangerous thing:
1- gauges, pump and ambient charts are a must for A/C work.
2- most systems have a hi/low 134a switch so compressor wont run if system is empty [so needs at least a can to start compressor when empty]
3- 40 lbs at rest means some 134a is in the system but not much.
4- Only hi/low pressure with compressor on means anything -- 0-10 is way low.
5- you only create vacuum to re-charge if system is empty. [new dryer/exp valve]
6- add 134a ONLY to low side.
7- engine RPMs a 1000, keep condenser cool --mist or fan.
8- dash fan on 3/4 of full
9- with a leak, you have lost compressor oil, for example, need to add 4-6 oz of PAG100.
Bottom-line: not too many pit-falls to just adding 134a with gauges but it would really be good to have someone knowledgeable to "fly co-pilot" with you the first time--IMHO....
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Old 09-19-2020, 04:52 PM   #9
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Does your system have a sight glass, if so, check to see if you see bubbles flashing, if so system is low on refrigerant.
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Old 09-19-2020, 04:58 PM   #10
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Quote:
Originally Posted by Old Scout View Post
I applaud you on your commitment to DIY--but a little knowledge can be a dangerous thing:
1- gauges, pump and ambient charts are a must for A/C work.
2- most systems have a hi/low 134a switch so compressor wont run if system is empty [so needs at least a can to start compressor when empty]
3- 40 lbs at rest means some 134a is in the system but not much.
4- Only hi/low pressure with compressor on means anything -- 0-10 is way low.
5- you only create vacuum to re-charge if system is empty. [new dryer/exp valve]
6- add 134a ONLY to low side.
7- engine RPMs a 1000, keep condenser cool --mist or fan.
8- dash fan on 3/4 of full
9- with a leak, you have lost compressor oil, for example, need to add 4-6 oz of PAG100.
Bottom-line: not too many pit-falls to just adding 134a with gauges but it would really be good to have someone knowledgeable to "fly co-pilot" with you the first time--IMHO....
Yep, got the gauges and vacuum pump if needed. Watched a bunch of YouTube videos, which helps...

Have been thinking about adding oil, most of the articles I saw advised against it? Even slight overfill hydro is compressor?

I also see that come cans of r134a have oil in them?
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Old 09-19-2020, 07:13 PM   #11
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You got a lot of help. Now we all have more info to better help. Dye in whatever charge cans is a good idea. Stay away from sealant/stop leak stuff. As far as oil there is way more oil in a DP than a car that would have leaked out.
I would always like to tune system when its actually hot outside keeping an eye on vent thermometer as I get close .
While it is cool out run vent on just cool no AC make sure there is no hot coolant sneaking by your heater control valve. Depending on rig you may be able to reach heater hose with your hand.
I'm able to tap pressure chart on phone and blow it up to read it without my readers..Or screenshot it go to gallery screenshots and blow it up bigger . On PC right click save to pics, a box will download in bottom left click it use pic slide tool blow up .
Edit I'm sorry ,trying to wrap my head around on how to actually use that chart in practice.
This is a rough gauge reading chart also shared.
Oops Can't add see below
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Old 09-19-2020, 08:05 PM   #12
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Hope this worksClick image for larger version

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Old 09-19-2020, 08:39 PM   #13
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Oh dear, so much conflicting information. I can't see any thing good coming out of this.
Temp time 2 plus 50? Where did this come from? Been in the trade 44 years and never heard that one before.
Good luck. You will need it. I'm confused myself.
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Old 09-19-2020, 09:23 PM   #14
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You have a leak. You need to deal with that first. Either with dye and enough 134 to keep the system running, or take it to a AC shop. It's illegal to dump R-134 into the atmosphere, I'd advise against it. Once you get the leak fixed, there should be a placard, or contact the manufacturer for how much R-134 to put into the system by weight. Put that much in, after vacuuming the system and verifying it holds vacuum. Done!
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