I have used the tool loaner program for a vacuum pump and hose manifold for checcking my a/c. The engine (340) in it is not the correct engine so I'm trying to locate the high and low side to hook this up. I took 2 pics of 1) my motor 2) the compressor witch has a fitting on each side of the picture right in the middle. The reading I've done suggested they would be of differing size but they seem the same. It could be from being R12 fittings instead of R134a...I'm not sure, but i would guess the one of the left would be high side. Any help? lol
High and Low side a/c
- Thread starter SixgunSal
- Start date
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67Dart273
Well-Known Member
Large tubing is low side. Small tubing is high. You have a shop manual? If not, download them free at MyMopar. No I don't work there. Some of those manuals got there because of some of the guys on here
Attempting to charge an AC system with a dimestore low side hose is no way to run a railroad
Attempting to charge an AC system with a dimestore low side hose is no way to run a railroad
Your fittings are the same size due to being R12 and not 134. The low side is the one on the passenger side of the compressor and the high side fitting is the one on the a/c muffler on the left side of the compressor. Chances are, you will have to add 134 fittings before you can attach any of your loaner tools the system.
Thank you for that shop manual link, I'm heading there now. You are right about the dimestore...either the red or blue both ends do not fit on high or low on the engine.
Thank you for that...if the guy would have told me I needed to put the converted fittings on I would have bought them while I was there...also the little rubber doughnuts that go in the fittings at the bottom to make an airtight seal are all broke so I need to see if o'reilly auto has spares. It's a conspiracy I swear.
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O'Reilly Auto Parts
sells spares
Tinmannz
Well-Known Member
Auto Zone part number is: LXVC-12 best I can tell. It’s literally no more than taking the Schrader cores out of the r12 fittings (please make sure it’s empty first), then screw the 134 fittings on top of them.
Charge through the low side.
There are threads here about converting but i can't find one.
67Dart273
Well-Known Member
The other thing here, is, you cannot just buy 134A conversion fittings and dump that refrigerant into an R12 system.
But 134A fittings --to hoses-- are standardized. The high side is stupidly larger, and red, and the low side is stupidly smaller, and blue. You cannot accidently interchange as with older R12 fittings, which were pretty much all 1/4 SAE flare, or no.4 SAE flare. That is NOT JIC and NOT AN. That is SAE
(Why stupidly? Because a low pressure system flows less than a high pressure one, the low side system should have a larger size port to flow quantity. If you are evacuating a system, the blue should have been larger. Stupid)
Some later model stuff, like my (former) 86 and 87 Rangers, had a proprietary small flare fitting on one side I don't remember which.
These are R12 manifold/ hose adapters.........to R134A system adapters
https://www.amazon.com/dp/B07T9HFBCH/?tag=fabo03-20
134a Quick Coupler, AC R134a Adapter Fittings Quick Connector, 1/4" SAE Male Flare High/Low A/C Freon Manifold Gauge Hose Conversion Kit
But 134A fittings --to hoses-- are standardized. The high side is stupidly larger, and red, and the low side is stupidly smaller, and blue. You cannot accidently interchange as with older R12 fittings, which were pretty much all 1/4 SAE flare, or no.4 SAE flare. That is NOT JIC and NOT AN. That is SAE
(Why stupidly? Because a low pressure system flows less than a high pressure one, the low side system should have a larger size port to flow quantity. If you are evacuating a system, the blue should have been larger. Stupid)
Some later model stuff, like my (former) 86 and 87 Rangers, had a proprietary small flare fitting on one side I don't remember which.
These are R12 manifold/ hose adapters.........to R134A system adapters
https://www.amazon.com/dp/B07T9HFBCH/?tag=fabo03-20
134a Quick Coupler, AC R134a Adapter Fittings Quick Connector, 1/4" SAE Male Flare High/Low A/C Freon Manifold Gauge Hose Conversion Kit
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Those are some good looking 90's. I got the fittings on - the high side would not take a shrader so I left it in the old fitting, and will find out when I put some gas in it if the red hose will still read. The blue one was pretty easy, I dremmeled down my smallest needle nose to make a tool. I keep wondering if I need to buy a cheapish manifold hose set for this. The manifold gage hoses I borrowed from Reilly's Auto has the rubber hose pieces that fit at the bottom inside all the hose hookups are broke and I've been running this vacuum pump for 2 hours and it won't get better then -15 - halfway to the 30 mark. I shut it off once and it didn't go back any so hopefully no leaks in the a/c. The searches I have done for only getting to -15 say its either the pump or the hose connections so thats why I wonder about the cheapish purchase of a manifold hose set. Is -15 good enough?
Pete in NH
Well-Known Member
HI,
From reading your posts I can see you're fairly new to automotive A/C work and very likely these old Mopar systems. So, here are a few things to consider. If you have no idea what is in the present system it would be a good idea to take it to an A/C shop or borrow a refrigerant identifier and see what is in the system. While it looks like the old R-12 fittings are still in place and not R-134A adapters that's no assurance of what some one may have put in there. There are many internet sites that will give you some basic ideas on automotive A/C systems and how they operate and reading the shop manual is a good place to start. If you do convert to R-134A stay away from those cheap/quick conversion kits out there. A/C professionals refer to them as "Death Kits" as they can quickly lead to system and compressor damage.
To convert to R-134A you will need to use the proper oil in the compressor, flush out the oil R-12 mineral type oil and refill with an R-134A compatible oil. I like to use an ester based oil with is compatible with both R-12 and R-134A. You will also need to change the receiver /drier to and R-134A compatible type. All new receiver/driers today are both R-12 and R-134 A compatible. If you don't do this the R-134A will bust the old desiccant bag in the drier and spread desiccant through out the system and you'll have a real mess. 15 inches of vacuum is no where low enough and some thing is not right some where. A good tight system will easily get down to 28 inches and hold that vacuum for many hours. You are not anywhere near being able to recharge your system and get good results when done. Good A/C work requires attention to detail, it's not hard to do but short cuts will only get you in expensive trouble.
67Dart273
Well-Known Member
I should have mentioned, there is a completely different approach which I like better, in some ways. The system I had which was converted, I DID NOT install R134A adapters on the system. I don't remember why, it may be some of the issues you are having.....they didn't fit correctly.
Anyhow, when I charged the system, I took a low side adapter and screwed it onto the middle port of my gauge manifold. Then just hooked the manifold to the old R12 flare fittings. This allows connecting an R134A can to the manifold, "easy."
Yes I am really new to automotive A/C, this and brakes I never really tried. I have ordered a receiver drier and will try an automotive shop tomorrow to see if I can schedule a vacuum for the dart. Would I have a vacuum done before or after installing the new receiver drier? The salesman at Autozone suggested the Pagoil
so that what I have but have not put in in yet. I'm pretty sure the vacuum and manifold gage hose set were not the best for me trying this out...not trying to make excuses, but some stuff is better left to the pros and I know I'm not one of them. lol Thanks for the good advice and it's a relief not to be banging my head against the wall another day (what they say about old dogs and new tricks sounds pretty good thou).
I always have the best luck charging through high side as a liquid (can or cylinder upside down).
Low side is liquid. High side is gas/vapor
Yup. I'm not arguin that. Just saying how I have the best luck. Sometimes I've found you have to do it to "shock" the compressor into starting. That's why I just went to charging through the high side only.
It's a wonder you don't lock up a compressor.
Never have. Not once.
67Dart273
Well-Known Member
NO IT IS NOT. the low side returning to the compressor is mostly cool but wet vapor, and must have some droplets to cool the compressor head and valves. On many systems this is checked/ established by superheat, which is the difference between the measured temperature of the tube (insulated) and the saturation temperature equivalent as read off the gauge/ chart at the pressure measured.
High side OUT OF THE COMPRESSOR is high pressure very high temp hot gas. After it leaves the condenser, it is cool, high pressure, liquid.
In a normal healthy system with good compressor valves, you will NEVER hurt a system by liquid charging the high side. The valves are what keeps liquid out of the compressor during shutdown, as it can migrate back from the condenser towards the compressor.
In my days servicing refrigeration/ HVAC stationary systems I have NEVER hurt a system by liquid charging into the high side.
You can liquid charge into the low side ONLY while in operation, and you must monitor operating pressures, use your head and ears, and meter the liquid so it does not "slug" the compressor. I have also done THAT lots of times, and NEVER slugged a compressor
YOU CAN NOT charge liquid or gas into the high side while in operation, unless it's pretty much empty and should not be running in that case. (Low pressure switch)
You can charge either liquid or gas into the low side while in operation. DO NOT charge liquid into the low side with the system off. If it gets to the compressor, it will sit there and when put into operation, it will hydraulic lock
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67Dart273 is spot on.
This is a little off base, but wanted to add, if you get a jug of 134a from a commercial supply house, it comes with the standard 1/4in. flare fitting, vs the 5/16? fitting used in automotive.
So with a commercial jug, you can use a standard r12 guage set for charging..... Not to mention, it is much cheaper....
This is a little off base, but wanted to add, if you get a jug of 134a from a commercial supply house, it comes with the standard 1/4in. flare fitting, vs the 5/16? fitting used in automotive.
So with a commercial jug, you can use a standard r12 guage set for charging..... Not to mention, it is much cheaper....
67Dart273
Well-Known Member
The 134 "jug" I bought (30lb) is NOT standard 1/4 flare. It is some special "new" fitting and required an adapter. The first one I bought off ebay did not fit. I don't know if it was the incorrect fitting, or just threaded wrong by the guy in the backyard shed in China. I don't know if some are different. "It would seem" that 134A would be "standardized" LOL
This is the adapter I needed and got 2nd try. What I needed was 1/2" Acme female (for the jug) and 1/4 male SAE (for the hoses/ manifold)
https://www.ebay.com/itm/New-FJC-6015-Air-Conditioning-R134A-1-2-Female-to-1-4-R12-Male-Flare-Adapter/183328909165?hash=item2aaf41276d:g
LEAAOSwR0hbTOzu
This is the adapter I needed and got 2nd try. What I needed was 1/2" Acme female (for the jug) and 1/4 male SAE (for the hoses/ manifold)
https://www.ebay.com/itm/New-FJC-6015-Air-Conditioning-R134A-1-2-Female-to-1-4-R12-Male-Flare-Adapter/183328909165?hash=item2aaf41276d:g
LEAAOSwR0hbTOzu
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Always good to learn something from a seasoned veteran. I wonder why they always call the low side the "liquid line"?
The 134a for commercial refrigeration is a different drum..... Below is a picture of the one I have currently.
BTW I just called my supplier and its $110.00 a drum.
67Dart273
Well-Known Member
I think you are confused, Mike. You have the output of the condenser, or if equipped the receiver dryer. That line is liquid and feeds the metering device which is immediately attached to the evaporator. The liquid boils to mostly vapor and a little liquid in the evap and continues to boil into more vapor / bit of liquid as it leaves the evap into the suction line. THAT is the low side. From there to the compressor, sometimes through an oil accumulator or other device. Out of the compressor is the "hot gas" line and goes back to the condenser. From the condenser the liquid goes (if equipped) into the receiver dryer.
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