Any A/C gurus out there?

f22beaver

TJ Enthusiast
Joined
Jul 6, 2021
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Location
Indianapolis
First off, yes, I know I should replace the dryer. So in the question below I know the answer is "replace the dryer" but also answering the question I'm actually asking will be much more helpful.

When I got my TJ the A/C Schrader valves were bad so the system was down/out on refrigerant. I replaced them and now it will hold vacuum without dropping over the course of a week or so.

My two questions then are;
1) Using the AutoZone rental manifold gauges and vacuum pump I can pull about 26" Hg and that's where it sticks. But it should pull 29 right? So is the 26 because of bad free loaner tools, a system fault, a bad part? Again, after I disconnect the vac pump and gauges the system will hold at the 25-26" range so it's not dropping like it has a leak.
2) Consider me a cynic, but before I spend the money to replace the dryer I'd like to run some UV dye through the system with new refrigerant to verify if, in fact, the system does maybe have a miniscule leak anywhere. What will be the impact on the system if I go ahead and send it with the existing dryer? Air won't be as cold? The streams will cross and my Jeep will implode?

Thanks for any input!
 
Not a guru.

I’d guess your loaner pump isn’t strong enough to pull the vacuum, or the gauge is off. If another pump isn’t an option, I’d replace the dryer and send it as-is. If you hold vacuum as you say, a leak is unlikely.

If the pump can’t get all the way down you’ll have — in theory — a minuscule amount of air in the system. Assuming so you’ll want/need a new dryer inline. It’s cheap insurance. Also only a few $$ more than two cans of r134 + dye.

Don’t forget to put an ounce or two of PAG oil in the new dryer when you install it.
 
If the pump can’t get all the way down you’ll have — in theory — a minuscule amount of air in the system. Assuming so you’ll want/need a new dryer inline. It’s cheap insurance. Also only a few $$ more than two cans of r134 + dye.
Noted and thank you. I think that's where my head was out. Also, my UV dye is also PAG oil so it will, by default, get a little extra oil.
 
the pump and gauges could be an issue, but if there is water in the system (such as the water that might have been absorbed by a dryer in a system that spent significant time open to atmosphere), pulling down and holding vacuum can be a challenge even without a leak until all of the water has evaporated and been removed by the vacuum pump. The same can be true with volatile substances like mineral spirits and other solvents - anything that is a liquid at 1 atmosphere but a vapor at 29" can slowly evaporate, constantly providing additional vapor volume for the pump to pull on until there's no more of the liquid left.

Food for thought.
 
the pump and gauges could be an issue, but if there is water in the system (such as the water that might have been absorbed by a dryer in a system that spent significant time open to atmosphere), pulling down and holding vacuum can be a challenge even without a leak until all of the water has evaporated and been removed by the vacuum pump. The same can be true with volatile substances like mineral spirits and other solvents - anything that is a liquid at 1 atmosphere but a vapor at 29" can slowly evaporate, constantly providing additional vapor volume for the pump to pull on until there's no more of the liquid left.

Food for thought.

That's a good train of thought there. I might throw the pump on another hour later tonight to see if it can boil off any more water.
 
Here's one for you in a/C 101, your TJ does not have a dryer if it's factory air ! It has a accumulator which is not a dryer, they do 2 completely different things. You need to replace the accumulator and flush that system and check that orifice tube and vacuum and fill with refrigerant and pag oil.
 
Here's one for you in a/C 101, your TJ does not have a dryer if it's factory air ! It has a accumulator which is not a dryer, they do 2 completely different things. You need to replace the accumulator and flush that system and check that orifice tube and vacuum and fill with refrigerant and pag oil.

TIL!! Thank you! Those are really not that expensive, seems like an easy proactive maintenance item.

Just for clarity, when you say "that orifice tube" you are referring to?
 
The orifice tube is located inside the liquid line which runs from condenser to evaporator, the tube is a filter and orifice or pressure dropping point. You need to back flush this line or replace.
 
R134a reacts with water to form hydrofluoric acid which damages the internal A/C components. This is why it is crucially important that R134a systems be properly evacuated (pumped down to boil off any moisture) and kept sealed. It is possible that the vacuum pump gauge is crap. Most of them are. Also most A/C accumulators have a desiccant bag inside them, which is why they should be replaced anytime the system is exposed to moisture. So, the accumulator is a kind of receiver drier.
 
The orifice tube is located inside the liquid line which runs from condenser to evaporator, the tube is a filter and orifice or pressure dropping point. You need to back flush this line or replace.
Thank you for pointing this out. I'm learning something new about A/C systems. Kind of sucks that the tube isn't a serviceable item. Do I have reason to think this part is clogged if no internals on my compressor/condensor/evap have gone bad? Or can the moisture that got in the system cause it to clog? I'm not trying to be overly cheap, but I just want to understand the risk. I'm not sure I want to spend the $50 on a new part, if I go the flush route do I flush from condensor to evap or evap to condensor?
R134a reacts with water to form hydrofluoric acid which damages the internal A/C components. This is why it is crucially important that R134a systems be properly evacuated (pumped down to boil off any moisture) and kept sealed. It is possible that the vacuum pump gauge is crap. Most of them are. Also most A/C accumulators have a desiccant bag inside them, which is why they should be replaced anytime the system is exposed to moisture. So, the accumulator is a kind of receiver drier.
Thanks for this info, I was actually reading a lot of your historical posts on A/C systems. I don't think anything outside of my Schraders were bad so I'm just sitting here weighing what else to do re: flush/changing lines. I'm definitely going to change the accumulator, that seems like an acceptable risk/benefit payoff.
 
R134a reacts with water to form hydrofluoric acid which damages the internal A/C components. This is why it is crucially important that R134a systems be properly evacuated (pumped down to boil off any moisture) and kept sealed. It is possible that the vacuum pump gauge is crap. Most of them are. Also most A/C accumulators have a desiccant bag inside them, which is why they should be replaced anytime the system is exposed to moisture. So, the accumulator is a kind of receiver drier.

Nailed it.
 
Quick update. Traded the pump at AutoZone for a newer one after I noticed some small oil leaks on the sight glass. New one immediately started pulling down 30" (or 29.9 if you want to be super pedantic). Currently running it for about an hour then going to let this sit for 24 hrs to make sure it holds then likely move forward with parts changes.
 
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Here's one for you in a/C 101, your TJ does not have a dryer if it's factory air ! It has a accumulator which is not a dryer, they do 2 completely different things. You need to replace the accumulator and flush that system and check that orifice tube and vacuum and fill with refrigerant and pag oil.

The accumulator is the dryer, it has a desiccant bag in it.
 
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The accumulator is the dryer, it has a desiccant bag in it.

The accumulator believe it or not accumulates liquid refrigerant and oil !
Reason being is a a/C compressor or any compressor cannot compress liquids. This is its primary job ! This believe it or not is why it's called a accumulator in a/ C world.
The compressor wouldn't last one trip without the accumulator doing its job turning the excess liquid refrigerant back to gas state!
True it does have a desiccant bag in it.
A a/c dryer is designed for a system with a Thermo Expansion Valve which a factory TJ does not have.
 
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The accumulator believe it or not accumulates liquid refrigerant and oil !
Reason being is a a/C compressor or any compressor cannot compress liquids. This is its primary job ! This believe it or not is why it's called a accumulator in a/ C world.
The compressor wouldn't last one trip without the accumulator doing its job turning the excess liquid refrigerant back to gas state!
True it does have a desiccant bag in it.
A a/c dryer is designed for a system with a Thermo Expansion Valve which a factory TJ does not have.

I know exactly what it does and it is an accumulator dryer to remove any moisture in the a/c system. A receiver dryer is installed on the liquid side of the system to store the liquid before the expansion valve. I have quite a bit of experience in automotive a/c.
 
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The accumulator believe it or not accumulates liquid refrigerant and oil !
Reason being is a a/C compressor or any compressor cannot compress liquids. This is its primary job ! This believe it or not is why it's called a accumulator in a/ C world.
The compressor wouldn't last one trip without the accumulator doing its job turning the excess liquid refrigerant back to gas state!
True it does have a desiccant bag in it.
A a/c dryer is designed for a system with a Thermo Expansion Valve which a factory TJ does not have.

I didn't see anybody presenting the accumulator as something other than what it is. But on that, containing a dessicant makes it an accumulator-dryer.

Plenty of systems don't have accumulators, in fact they're not actually used very often in comfort cooling AC applications where the load and operating conditions are fairly stable. Where you see them is primarily in automotive where there is a fixed expansion device and loads vary from 100 ambient with high humidity, down to the depths of winter when the defogger is on. They're also used a lot in refrigeration which experiences large load shifts when portions of the system enter and exit defrost cycles.
 
I didn't see anybody presenting the accumulator as something other than what it is. But on that, containing a dessicant makes it an accumulator-dryer.

Plenty of systems don't have accumulators, in fact they're not actually used very often in comfort cooling AC applications where the load and operating conditions are fairly stable. Where you see them is primarily in automotive where there is a fixed expansion device and loads vary from 100 ambient with high humidity, down to the depths of winter when the defogger is on. They're also used a lot in refrigeration which experiences large load shifts when portions of the system enter and exit defrost cycles
You obviously didn't read the first sentence of the post. He didn't know much about a/c so I was giving him some 101.
Jeep TJ has a accumulator , which is a vital part of Orifice tube system. With that said I call Monkeys Uncle and you can call it whatever you want !
 
You obviously didn't read the first sentence of the post. He didn't know much about a/c so I was giving him some 101.
Jeep TJ has a accumulator , which is a vital part of Orifice tube system. With that said I call Monkeys Uncle and you can call it whatever you want !

I do know about automotive A/c systems, your statement “The tj does not have a dryer” is false and misleading. If it was only an accumulator ( round chamber with a pipe inside) why would there be a recommendation to replace it if the system was left open?
 
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First off, yes, I know I should replace the dryer. So in the question below I know the answer is "replace the dryer" but also answering the question I'm actually asking will be much more helpful.

When I got my TJ the A/C Schrader valves were bad so the system was down/out on refrigerant. I replaced them and now it will hold vacuum without dropping over the course of a week or so.

My two questions then are;
1) Using the AutoZone rental manifold gauges and vacuum pump I can pull about 26" Hg and that's where it sticks. But it should pull 29 right? So is the 26 because of bad free loaner tools, a system fault, a bad part? Again, after I disconnect the vac pump and gauges the system will hold at the 25-26" range so it's not dropping like it has a leak.
2) Consider me a cynic, but before I spend the money to replace the dryer I'd like to run some UV dye through the system with new refrigerant to verify if, in fact, the system does maybe have a miniscule leak anywhere. What will be the impact on the system if I go ahead and send it with the existing dryer? Air won't be as cold? The streams will cross and my Jeep will implode?

Thanks for any input!
@f22beaver couple questions.
Was the system completely empty or did it have a small amount of pressure?
Can you rotate the compressor clutch or is the compressor locked up?
This is the way I would approach this on my vehicle. I would evacuate the system. I would then charge it with the dye. I would then drive it for a week or two if the system is operating properly. I would then purchase the accumulator and o rings for all the connections. Then check for any leaks at connections or the condenser. I would also remove the compressor clutch ( don’t loose adjustment shims) to check for a shaft seal leak. Then I would run it at idle with the blower on high for about 20 minutes Jen discharge the system to replace o rings and the accumulator. When you remove the lines to replace o rings take a good look inside of them for any contamination (metal or sand) metal would be from the compressor and sand would be desiccant from the accumulator, either one of these and you would need to replace components. As far as the orfice in the liquid line it really cannot go bad by itself. It is just a metal tube with a filter around it. It will catch small debris. If it is plugged from major debris you should know it when you are charging the system as the high pressure will be high and low side will be low. When you replace the accumulator drain and measure the oil so you can add the same amount to the new one or check if it came with oil in it. Evacuate and recharge and set the clutch gap when you reinstall the clutch. As far as flushing the system I would stay away from that unless you have contamination, I just have not seen over the counter flushes that would do a good job and removing all the flush can be tricky. I use to use a recirculating flush pump with special solvent to do components individually but it was very time consuming. If compressed air is used to try and back flush the liquid line you most likely willl damage the orfice. I hope this helps and is the information you need. Message me if you have any additional questions, I will try to steer you in the right direction.