finding AC leak with no pressure in system

[ElFenix]

my slow leak finally turned into a major leak. there is 0 pressure in the system currently. i assume the usual warnings about charging the system while the compressor is engaged are there to keep the system from blowing back/leaking, which isn't a concern when there's 0 pressure, so i can (attempt) charging the system. correct? i'll be going to an AC shop but this will at least let me know where the leak is myself (so if it's the condenser but they tell me it's the compressor i can tell them to f off) and maybe fast forward the process.

 

[boomerang]

The compressor clutch will not engage until there is sufficient pressure in the system and in fact, the compressor must be engaged to properly charge the system. I am curious how you are going to determine where the leak is.

 

[C1]

Typically there is AC oil where seen at the refrigerant leak site, so inspect carefully.

Go to a place like Autozone and purchase a fluro dye kit for AC then add the dye along with some freon to the system to trace the leak(s).

You should easily be able to temporarily by pass the AC low pressure cut out switch. (Just remove the connector at the clutch and apply 12v battery current to he clutch terminals.)

 

[ElFenix]

Yeah I should have used dye when I recharged it last week. I thought I'd left it in the car and didn't want to go back into the building to get it. The prior charge had lasted 5 months.

I was going to dye it then attempt a charge - wouldn't the charge be enough to start raising the pressure and get the clutch to engage? None of the YouTube U videos have people bypassing the switch.

 

[bruceb]

You can use a vacuum pump. If it does not hold vacuum, then it has a leak. You should be able to find it that way. If not, then you could add 1 can R134A (it can go in liquid via the low side port) provided the system is not running. That should be enough to let the compressor engage. If you use the dye, you need a UV Flashlight and the goggles to see the dye (best done when it is dark, it will glow a yellowish green)

 

[ElFenix]

i has no vacuum pump nor a convenient electrical outlet in the parking garage for my building. dye was apparent enough on my gloved finger using just the flashlight in the dark, so i think i'll be fine without special goggles (they do nothing!)

 

[boomerang]

You'll want the compressor to engage in order to get the dye circulating. If one can of refrigerant is enough, great. If not, you'll need to add more.

Be aware that if the leak is in the evaporator, you will not be able to see the dye without considerable disassembly behind the dash. In other words, the dye may not do you any good which is why I asked how you were going to determine where the leak was. A shop that does A/C repair would typically use a sniffer to find a leak.

Also be aware that the shop may tell you that the accumulator needs to be replaced as part of the repair. With no pressure in the system along with the introduction of cans of auto parts store purchased refrigerant there is a very real possibility that the desiccant in the accumulator (sometimes called a receiver/dryer) is saturated. Moisture is the enemy of A/C systems. It will allow for the formation of acids that will eat the aluminum components of an A/C system from the inside out.

Prior to charging the system after the repair, the shop will hook up a vacuum pump to see if the system will hold a vacuum. That vacuum should "boil off" the moisture trapped in the accumulator but there is no way to actually tell if it was entirely successful. Because the shop has to warranty the repair, replacing the accumulator may not be an option.

 

[ISAslot]

If you can find an outlet/power source, you can borrow a vacuum pump from Autozone.

 

[Paperdoc]

In a shop the tech would first use a vacuum pump and tank to remove any old refrigerant gas and store it (not releasing it to atmosphere - it's a gas that contributes to ozone layer depletion), then leave the pump on the system for a while to see how low the vacuum pressure can go, and how quickly. Then they close valves and shut off the pump to see whether the system pressure rises again indicating a leak. They know the normal actual "good" pressure for a vacuum and how long such pumping and leaking should take in a no-leak system. I you do NOT know those things, how do you plan to use a borrowed vacuum pump to test?

Last time I had this trouble (this past spring on my wife's old car) the tech verified there was clearly a leak, but could not find it by inspection or listening for a hiss. So he added fluorescent dye and refrigerant and told me to come back when the system showed poor cooling agin. That took less than a week. THEN he used a UV lamp to find a leak in a high-pressure hose from compressor to condenser. When I got a replacement hose and he installed it, problem solved.

 

[ElFenix]

leak was in high pressure hose and was apparent enough to someone who knew what he was looking for that he had it diagnosed in ~2 minutes w/o dye (even told me that wasn't how it worked when i suggested adding dye and refrigerant and seeing where it leaked out overnight).

 

[Paperdoc]

Yeah, with any small leak "overnight" probably would not be enough time for the leak to release enough dye to find. In my case the advice was "until the system fails to get cold", and that took nearly a week.Then the dye was easy to spot with the UV lamp. My tech was pretty sure it was near the condenser at the front by the rad, but could not see it without the dye. Of course, as someone above pointed out, if the leak had been inside the heater housing in the evaporator unit, the only way to find that would have been to rip all that heater ductwork apart.