Automotive AC troubleshooting 101 - help me get started?

[SC Maintenance]

Another question - I couldn't decide if I should spring for a good pump or go cheap. At the last minute I just went and got the 2 stage from harbor freight - but it pukes out enough oil vapor to fog up my whole garage in minutes. Do they all do this - or is this as bad as it seems?

You can sort of see the fog exiting in this pic - but it really doesn't do it justice. I though my glasses were dirty and went and cleaned them!

 

[Nukeman7]

So I finally got everything, and connected it up, and the pump was not pulling any vacuum. It appears all my hoses have what appears to be a schrader valve in them. When I connect the yellow hose to the pump, no vacuum comes out the other end of the hose. I tried to remove the schrader valve - all it does is spin forever in both directions?

What am I doing wrong?

Edit - OK some quick trouble shooting - I swapped the red hose for the yellow hose - left closed the red valve. Its now pulling a vacuum on the system. I assume my hello hose is fubar?

The yellow hose might or might not be bad. Without seeing your exact setup, I can't tell if your hose is directional. However, the hose end with the depressor tang (see right connector in photo below) connects to the vacuum pump/freon tank and the open hose end (see left coupling in photo) connects to the center manifold port coupling.

Also while I am here, when I eventually get to pulling a vacuum - do I pull from both sides - ie both valves open - or only on the low pressure blue side?

Most pros prefer to draw suction from both the low and high pressure side because it will draw down quicker and some claim it removes moisture more equally. I normally pull from both hoses, but have drawn from a single hose when not in a hurry. When changing major components, I draw it down to -29.9+ in.Hg and isolate/shut down the pump for 15 minutes to see if there is loss of vacuum (indicating a leak in the system). If it holds vacuum after 15 minutes, I will re-engage the pump for another 45 minutes to ensure the system is fully dry. Be sure to close all isolation valves (starting at the QD ports) before shutting off the pump for the final time. Verify no loss of suction for ~10 minutes before you charge with the refrigerant.

 

[Nukeman7]

Another question - I couldn't decide if I should spring for a good pump or go cheap. At the last minute I just went and got the 2 stage from harbor freight - but it pukes out enough oil vapor to fog up my whole garage in minutes. Do they all do this - or is this as bad as it seems?

You can sort of see the fog exiting in this pic - but it really doesn't do it justice. I though my glasses were dirty and went and cleaned them!

That photo looks normal if the system is highly saturated with moist humid air. The longer you vacuum, the less vapor you will see. However, it should not fog up your whole garage.

 

[Astro14]

it seems like it’s the local municipality or states that dictate whether a leak needs to be found.
The EPA appears to have no such mandate for vehicles, at least according to this Google AI result.

View attachment 280258

I believe that leak repair prior to charging a system IS Federally mandated.

You can’t trust AI.

Part of the reason we don’t like it being posted.

A section 609 certified technician will not add refrigerant to a system that is leaking.

https://www.epa.gov/mvac/regulatory-requirements-mvac-system-servicing

Private owners adding refrigerant are bound by the same ELA regulations, even though they don’t have the 609 certification.

 

[SC Maintenance]

The yellow hose might or might not be bad. Without seeing your exact setup, I can't tell if your hose is directional. However, the hose end with the depressor tang (see right connector in photo below) connects to the vacuum pump/freon tank and the open hose end (see left coupling in photo) connects to the center manifold port coupling.
View attachment 283660


Most pros prefer to draw suction from both the low and high pressure side because it will draw down quicker and some claim it removes moisture more equally. I normally pull from both hoses, but have drawn from a single hose when not in a hurry. When changing major components, I draw it down to -29.9+ in.Hg and isolate/shut down the pump for 15 minutes to see if there is loss of vacuum (indicating a leak in the system). If it holds vacuum after 15 minutes, I will re-engage the pump for another 45 minutes to ensure the system is fully dry. Be sure to close all isolation valves (starting at the QD ports) before shutting off the pump for the final time. Verify no loss of suction for ~10 minutes before you charge with the refrigerant.

So after I posted this, I messed with it some more. The Schrader end was connected to the pump. It has a different thread than all the other hoses and the other end of itself, and it also has a 45 degree angle. I was able to connect the other end without the depressor tang to the other port on the pump and then with the pump running push on it with a Schrader valve tool. Sometimes it would push in and allow a little vacuum, but not much. I believe that valve is not working given I was able to get the red hose - which also has a valve - to work. But of course I am not an expert.

On the pump I think it was water vapor, but it was also puking oil, so I think it was a combo. The pump instructions said to check the o-ring - which looked fine to me but again I don't really know what I am doing. I believe it might just be the cap. However its supposed to work to keep the oil in, it seems not to be? I might just try to return this one and see what they say.

Thank you again for your help!

 

[CarlB]

Be a steward of the environment, and try to avoid venting.

This opening scene from Dirty Jobs. I didn't realize it until recently, but that big cloud of white is the guy cutting the refrigerant lines. I wonder if they ever received a visit from the EPA.

View attachment 280344

No, because no one cares about 16oz. Imagine citing people for venting after a front end collision or an oring going bad.

 

[SC Maintenance]

No, because no one cares about 16oz. Imagine citing people for venting after a front end collision or an oring going bad.

I was in walmart and they literally have an entire end-cap of 16oz 134 cans. Must be 1000 of them or more. I am sure all of those are going into completely sealed systems every spring

 

[SC Maintenance]

I pulled a vacuum for about 10 minutes and closed the valve. It immediately dropped to -10 and dissipated from there in about 20 seconds.

So obviously a large leak.

So I can either find someone to pay to charge with nitrogen and give me a diagnosis - which will be tough around here. I could go against everyone's advice and pressurize it with air. Given how long its been unsealed I really don't know what the harm at this point. Or I could just throw a new condenser in and hope for the best, there not expensive and it would seem that a leak that large would need to be something other than an o-ring or compressor shaft seal, so that would be the logical starting point for the parts canon.

Decisions.

 

[CarlB]

I pulled a vacuum for about 10 minutes and closed the valve. It immediately dropped to -10 and dissipated from there in about 20 seconds.

So obviously a large leak.

So I can either find someone to pay to charge with nitrogen and give me a diagnosis - which will be tough around here. I could go against everyone's advice and pressurize it with air. Given how long its been unsealed I really don't know what the harm at this point. Or I could just throw a new condenser in and hope for the best, there not expensive and it would seem that a leak that large would need to be something other than an o-ring or compressor shaft seal, so that would be the logical starting point for the parts canon.

Decisions.

I use UV dye to find big leaks. Electronic flourocarbon detector for the small ones.

 

[Mechanician]

so that would be the logical starting point for the parts canon.

Decisions.

The only real problem with a parts canon (other than wallet drain) is the possibility of introducing an additional problem to the original problem, given the current state of cheap replacement part reliability.
The price you're gambling is pretty small, and you can verify if the leak is gone afterward with the same vacuum test. (IF your setup itself isn't what's leaking)
I would try using a little pressure and soapy water first, if it were in my charge.
But I would recommend not going wild with the shotgun approach, and possibly installing multiple new problems.
You may also want to obtain/install dye if it's not currently in the system, to make your life easier in the future in any case.

 

[Mechanician]

With a big leak there's usually an oil spot in the fins somewhere on the condenser. Try using a light and shining it from different angles.

 

[Mazomopar]

I wish a Ford and a Chevy would still last ten years, like they should.

It always sounded like "Chivvy" to me..

 

[SC Maintenance]

With a big leak there's usually an oil spot in the fins somewhere on the condenser. Try using a light and shining it from different angles.

I bought a UV flashlight and yellow glasses and looked all around. It was supposed to have dye in it from the factory. I did see what seemed like corrosion / white UV around one end of the condenser, but no oil, no yellow dye, and nothing that appeared to be a stone.

 

[Mechanician]

I bought a UV flashlight and yellow glasses and looked all around. It was supposed to have dye in it from the factory. I did see what seemed like corrosion / white UV around one end of the condenser, but no oil, no yellow dye, and nothing that appeared to be a stone.

I have never heard of factory installed dye, learned something. You can get some weird glows off of things at times that mean nothing.
If it isn't leaking at any of the lines - or a hose isn't wet - you've probably got an evaporator, or H block/expansion valve leaking.
Although a big leak at either of those would be quite unusual.
A large leak at the compressor would also be unusual. - I have seen some with a "blow-off" relief valve on the compressor that pops after a condenser fan failure.
If it has factory dye, and the evaporator is leaking, you MAY see some dye at the drain tube. My experience has been maybe 50-50 of evaporator leak dye showing up at the drain. Also often the H block is actually under the hood, covered in an insulating foam.
If you also purchased a sniffer you can sometimes pick up an evaporator leak at a vent, after leaving it set off for a bit, then turning on the blower.
Sometimes you can get a peek into the evaporator plenum by removing the blower housing.
And sometimes finding an evaporator leak is a matter of eliminating everything else, before disassembly.

 

[SC Maintenance]

I have never heard of factory installed dye, learned something. You can get some weird glows off of things at times that mean nothing.
If it isn't leaking at any of the lines - or a hose isn't wet - you've probably got an evaporator, or H block/expansion valve leaking.
Although a big leak at either of those would be quite unusual.
A large leak at the compressor would also be unusual. - I have seen some with a "blow-off" relief valve on the compressor that pops after a condenser fan failure.
If it has factory dye, and the evaporator is leaking, you MAY see some dye at the drain tube. My experience has been maybe 50-50 of evaporator leak dye showing up at the drain. Also often the H block is actually under the hood, covered in an insulating foam.
If you also purchased a sniffer you can sometimes pick up an evaporator leak at a vent, after leaving it set off for a bit, then turning on the blower.
Sometimes you can get a peek into the evaporator plenum by removing the blower housing.
And sometimes finding an evaporator leak is a matter of eliminating everything else, before disassembly.

Well according the the factory service manual, but who really knows? Does Dye last 17 years?

"• The A/C system contains a fluorescent leak detection dye used for locating refrigerant leaks. An ultraviolet
(UV) lamp is required to illuminate the dye when inspecting for leaks."

I think I am going to need to get plumbed up to put pressure on it. I am already planning on changing the desicant canister once I figure things out. The evaporator coil isn't as hard to get to as some - flat rate for the heater core / evap coil is I think 8 hours. The dash and everything has to come out, but I have communicated with a couple guys on the Nissan boards that have done it and they say its not all that bad - just a lot of time.

 

[Nukeman7]

Well according the the factory service manual, but who really knows? Does Dye last 17 years?

"• The A/C system contains a fluorescent leak detection dye used for locating refrigerant leaks. An ultraviolet
(UV) lamp is required to illuminate the dye when inspecting for leaks."

I think I am going to need to get plumbed up to put pressure on it. I am already planning on changing the desicant canister once I figure things out. The evaporator coil isn't as hard to get to as some - flat rate for the heater core / evap coil is I think 8 hours. The dash and everything has to come out, but I have communicated with a couple guys on the Nissan boards that have done it and they say its not all that bad - just a lot of time.

I have a 2000 Xterra and a 2005 Frontier and neither vehicle came from the factory with UV dye in the PAG 46 oil. You can remove the low pressure side Schrader valve and shine the UV flashlight in the orifice. If you don't see any flourescent yellow-green illumination, the oil has no dye. Yes, the dye will last forever unless the entire system is flushed with solvent.

Also, I think the odds are low that the leak is in the evaporator. More likely to be corrosion/damage to the condenser or an o-ring/hose crimp leak. As stated in Post #71, also look for signs of faint oil film stains around couplings, mechanical joints and the compressor seals.

 

[zzyzzx]

I was in walmart and they literally have an entire end-cap of 16oz 134 cans. Must be 1000 of them or more. I am sure all of those are going into completely sealed systems every spring

Are you sure that they aren't 12oz cans? You know because of shrinkflation.

 

[mk378]

If there's factory dye you will see it in the service ports under the cap. Dye rides in the oil. If there is a leak while the system is not running, it is quite possible that only gas will escape.

It is legal to use R-134a as a leak testing agent along with a refrigerant detector. It only takes an oz or so to put a positive pressure in the system. When there is a big leak, use very little pressure or it will fill up the whole garage and your leak detector will give false alarms.

The regular cans have always been 12 oz. Way back when R-12 was sold to DIYers, those cans were also 12 oz.

 

[SC Maintenance]

I found the leak - or at least one of them. I am almost certain its from here - the low pressure suction joint at the compressor. It doesn't seem to be coming from the shaft seal. Its definitely coming from one of them - the leak detector hits hardest here.

So I think the best way to replace this is to remove this hose completely rather than trying to do it blind or hang upside down. Its about 2 feet long and the top end is easily accessible. I guess I need to figure out more tools / parts:

1) Someone mentioned do not use a metal pic. Should I get something like a nylon dental pic?
2) o-rings? Nissan says to always replace them in the manual - but they don't sell them. Are these things sized pretty standard?
3) seems like there is lots of oil in this joint already. Should I try to use nylog blue which I haven't gotten yet, or just put pag oil on the o-ring?

I also need to order a new desiccant canister, a new vacuum pump - I returned the harbor freight one I didn't like. No questions asked. I guess I see why people like that place.

I also need to figure out my gauge set. I can return it and get another, or just buy a new yellow hose. Do all yellow hoses have a one way valve in them? Seems like a liability?

AC joint IMG_3617.webp

• SC Maintenance
• Jun 10, 2025

AC joint IMG_3622.webp

• SC Maintenance
• Jun 10, 2025

 

[Mechanician]

A large leak from an intact O ring?
PAG oil is good enough, O rings come in standard sizes, any dull tool will work fine to remove the O ring, maybe a zip tie.
How did the soapy water indicate when sprayed there?
Is there dye there, or inside the joint?