Automotive AC troubleshooting 101 - help me get started?

[SC Maintenance]

So while I understand the parts of an Automotive AC system quite well, I have no real practical experience because I haven't had many problems. My Xterra AC quite working one day - more or less overnight my daughter tells me ?

Put a cheap refill gauge on it and the system is empty it appears.

Is my first step to pull a vacuum on it and hopefully find / hear something?

Or do I pull a vacuum, fill it with refrigerant and die, and hope I can see it?

Suggestions on a guage set and vacuum pump? Is the Harbor Freight stuff acceptable, or the cheap stuff on Amazon, or should I look elsehwere?

 

[Nukeman7]

I'd suggest getting the loaner A/C gauge set and vacuum pump from Autozone or O'Reillys for free. Don't buy the equipment if this is a one time repair. If you decide later to get the gauges, buy a quality set like a MasterCool or Yellowjacket.

You need to verify both high side and low side pressures before searching for a leak. If it actually went to zero psi overnight, you may have a hole in the condenser from a rock strike. You can find large leaks just by charging the system with R-134a (preferably with UV dye), but I recommend the following inexpensive freon detector from Amazon when searching for small leaks.

 

[Mechanician]

Start by looking for any oil film on the lines, and other parts (compressor, condenser, drier) - under the hood.
I've found many leaks this way.
Also you can put just a little refrigerant in, then spray the parts down with soapy water.
The fact it's empty, means it's a significant leak. Maybe a rock hit the condenser?

 

[SC Maintenance]

I'd suggest getting the loaner A/C gauge set and vacuum pump from Autozone or O'Reillys for free

My experience on loaner tools is poor - broken, missing pieces. I would rather buy something - and sell it after or even give it away. Just the way I am wired. Still, I believe I will likely need it again once I know what I am doing.

The fact it's empty, means it's a significant leak. Maybe a rock hit the condenser?

The grill pops off pretty easily and I have a really good view of the condensor. I don't see any spots with oil or anything on the front.

Could be condensor?

I had a indy shop replace the heater core years ago - for the specific reason that the A/C system needs to be purged and recharged. Possibly they put UV dye in when they refilled? Maybe I should get a black light and yellow glasses to look around?

 

[Chris142]

By law the first thing is to pressure test it with at least 100 psi of nitrogen and spray it with soap to look for leaks. If none found look at all hoses and connections for signs of oil or dye . Then replace the Schrader valves,vacuum and see if it drops. If it does not drop add 2 oz of ester oil and ac dye. Charge to spec,run it 30/45 min and look for leaks.

I have found most leaks are from the schraders.

What kind of car?

 

[SC Maintenance]

By law the first thing is to pressure test it with at least 100 psi of nitrogen and spray it with soap to look for leaks. If none found look at all hoses and connections for signs of oil or dye . Then replace the Schrader valves,vacuum and see if it drops. If it does not drop add 2 oz of ester oil and ac dye. Charge to spec,run it 30/45 min and look for leaks.

I have found most leaks are from the schraders.

What kind of car?

Its for my high mile 2008 Xterra in my sig above.

Do you use a specific brand of Schrader valve?

 

[Mechanician]

The failure you describe would likely mean a big leak.
Slow leaks like valves, and seals usually reveal themselves with poor cooling - low - not a suddenly empty system. - Usually
The fact you're not seeing anything on the condenser is good. Yes the UV, and glasses is worth a try.
Since it's already empty if there's a joint that's easily accessed, you can take a peak inside for dye. (You can also add dye that way.)

 

[SC Maintenance]

The failure you describe would likely mean a big leak.

Suddenly may not have meant like driving down the road and it stopped. My daughter drives this car, and it can sit for several days. Also it "quit" mid April and we had a pretty cool spring, so its certainly possible that it drained over a bit of time and she finally noticed. The car is coming home for the summer so I can now actually work on it. It is definitely empty now - no pressure at all.

Since it's already empty if there's a joint that's easily accessed, you can take a peak inside for dye. (You can also add dye that way.)

Is there a benefit to splitting a joint vs just removing a Schrader valve?

 

[Mechanician]

Suddenly may not have meant like driving down the road and it stopped. My daughter drives this car, and it can sit for several days. Also it "quit" mid April and we had a pretty cool spring, so its certainly possible that it drained over a bit of time and she finally noticed. The car is coming home for the summer so I can now actually work on it. It is definitely empty now - no pressure at all.

Is there a benefit to splitting a joint vs just removing a Schrader valve?

Ahh.. I read it quit working one day - but still completely empty means a bad leak.
No real benefit unless you want to add dye, remember that anything you open may start to leak, so whatever is easiest to inspect.
If there's a hose to pipe connection that's easily opened, that's where I would look, the "o" ring is easily inspected too.
I'm sure you know all the sayings about old plumbing

 

[Mechanician]

"Ususally" when a system leaks while sitting for a season, there's at least a little pressure left behind.
Also remember that when it's completely empty the drier, or desiccant should be replaced.

 

[CarbonToast]

By law the first thing is to pressure test it with at least 100 psi of nitrogen and spray it with soap to look for leaks. If none found look at all hoses and connections for signs of oil or dye . Then replace the Schrader valves,vacuum and see if it drops. If it does not drop add 2 oz of ester oil and ac dye. Charge to spec,run it 30/45 min and look for leaks.

I have found most leaks are from the schraders.

What kind of car?

As a shade tree, couldn't you just use like ~50psi or so off a air compressor? That should be plenty for a soap spray test.

Not perfect, but access to 100psi of nitrogen is limited.You need to replace dessicant and pull a vacuum anyways which will boil off the water.

 

[SC Maintenance]

"Ususally" when a system leaks while sitting for a season, there's at least a little pressure left behind.
Also remember that when it's completely empty the drier, or desiccant should be replaced.

I don't think there is a way to replace just the desiccant. The dryer is integral to the condenser.

 

[Astro14]

As a shade tree, couldn't you just use like ~50psi or so off a air compressor? That should be plenty for a soap spray test.

Not perfect, but access to 100psi of nitrogen is limited.You need to replace dessicant and pull a vacuum anyways which will boil off the water.

This isn’t a shade tree v. Professional discussion.

It’s an EPA regulation discussion. In order to legally work on AC systems, and to buy refrigerant in quantity, you have to pass the EPA 609 certification, which stipulates how systems are to be handled, tested, and repaired.

Also, the high side runs closer to 200 PSI, so a 50 PSI test may not reveal the leak.

 

[Mechanician]

I don't think there is a way to replace just the desiccant. The dryer is integral to the condenser.

You are correct - most cars don't use a replaceable desiccant bag. But the drier should be replaced if the system has been empty for any period. Humidity has had time to get in the system.
There are vacuum pumps, that are capable of pulling all moisture out, and gauges sensitive enough to verify that - but a drier would still be recommended, and cheaper anyway.
You are not required to have a certification to repair your personal vehicle's A/C system.
But the regulations are all about not releasing refrigerant to the atmosphere. So don't do that.

 

[Chris142]

Its for my high mile 2008 Xterra in my sig above.

Do you use a specific brand of Schrader valve?

Odd as I can't see sigs on my phone for some reason. You can buy the and caps and valves kit @ any auto parts store. Look at the high side hose on that truck. That's usually the leaker on those.

 

[Chris142]

I don't think there is a way to replace just the desiccant. The dryer is integral to the condenser.


View attachment 279889

It un bolts.

 

[SC Maintenance]

It un bolts.

View attachment 279902

I assume this is solder on - which would be well beyond my skill set.

A new condenser is $100 from Koyo - so possibly I just change the whole thing if I get the actual problem figured out?

 

[Chris142]

I assume this is solder on - which would be well beyond my skill set.

A new condenser is $100 from Koyo - so possibly I just change the whole thing if I get the actual problem figured out?

No it unbolts with bolts

 

[Nukeman7]

I assume this is solder on - which would be well beyond my skill set.

A new condenser is $100 from Koyo - so possibly I just change the whole thing if I get the actual problem figured out?

It is not a solder on drier. It has O-rings on each penetration nipple and the coupling is secured with a single 10mm bolt. I have the same setup on the VQ40DE engine in my 2005 Nissan Frontier.

 

[iCurious]

If the Schrader valves are actually leaking, you can confirm this with the system running while spraying soapy water see if it bubbles. I highly doubt it is the case. I am thinking the leak is elsewhere.