How should I proceed with my very low AC

[Previologist]

I still see a little silvery something zooming through the sight glass, but I have zero cold air. I could pull a vacuum and refill and replace the dryer it if I knew it was empty, but since it doesn't appear to be 100% empty I'm wondering what my steps should be. Don't want to take it to a shop can't afford it. Should I shoot some dye and/or sealant in it and hope for the best while expecting the worst? Or?

 

[ArthurKotb]

I assume you still have Freon in there? If so, I would open the schrader valve and let whatever is left in there out. I'd replace it with R134a that has a self-sealer and wait to see what happens... but that's me.

 

[alumarine]

I'd stay away from sealer unless you never plan to fix it right.
Can you not buy R134a where you live and a cheap hose with a gauge that goes on the can?
I thought Walmart sold that stuff.
Just add a bit at a time.

That's not the best way but it might work and doesn't cost much.

 

[JohnMc]

If you crank the temp knob all the way cold and turn the A/C on, what does the compressor do? Kick on for a second and kick back off? Cycle off and on? Not turn on at all?

R134a systems will not run the compressor is the pressure on the low (suction) side is too low, because the compressor relies on oil carried around by the R134a for lubrication.

If you have any pressure in the system at all, that's a good sign, no real need to evacuate and pull a vacuum on it, the fact that it's held pressure for years is a great sign.

Get a cheap gauge and hook it up to the low pressure side and see what that shows. If it's low, add a can. That's like 75% of 'no A/C' issues right there. An extremely low leak that's gotten the pressure too low after a couple of decades.

My wife's '96 had an unusual failure (I think? I'm certainly no A/C expert) where the expansion valve stuck shut. Plenty of pressure in the system, but the compressor would just run for a couple of seconds and then shut off and not come back on. Which at first glance seems like low pressure. But I have a cheap set of Amazon gauges (the manifold, lines, and a high pressure and low pressure gauge) and it showed the low prssure going down low enough to shut the compressor off, and the high pressure side spiking really high, and then staying that way. She took it to an A/C place, had them remove the R134a from the system, then brought it back home and replaced the expansion valve and dryer, then took it back to them for a recharge (cheaper because they reused the R134a that was in it before).

If there's no pressure in the system then you have to find the leak.

 

[Previologist]

I'd stay away from sealer unless you never plan to fix it right.
Can you not buy R134a where you live and a cheap hose with a gauge that goes on the can?
I thought Walmart sold that stuff.
Just add a bit at a time.

That's not the best way but it might work and doesn't cost much.

Of course I have access to cans of 134a.

But its not a question of how to top it off, its a question of what to do with a system that may have a significant leak, or other problem. I've topped it off multiple times over the years but never had zero cold air before.

 

[Previologist]

If you crank the temp knob all the way cold and turn the A/C on, what does the compressor do? Kick on for a second and kick back off? Cycle off and on? Not turn on at all?

None of the above. It doesn't turn off at all, when the AC is on. At least for the 5 minutes I ran it just now.

R134a systems will not run the compressor is the pressure on the low (suction) side is too low, because the compressor relies on oil carried around by the R134a for lubrication.

If you have any pressure in the system at all, that's a good sign, no real need to evacuate and pull a vacuum on it, the fact that it's held pressure for years is a great sign.

Get a cheap gauge and hook it up to the low pressure side and see what that shows. If it's low, add a can. That's like 75% of 'no A/C' issues right there.

Pretty sure I did that last year with little to no effect.

An extremely low leak that's gotten the pressure too low after a couple of decades.

I've recharged it at least several times in the past. What I see in the sight glass is minimal. I see something, but its almost nothing. Not at all what it usually looks like. I suspect when I recharged it last year the pressure was enough to cause it to leak past a bad seal, but once it leaked out a small amount still remained. That's just a guess. I could always waste another can to find out but
its not only wasteful it's irresponsible, if there is a leak.

 

[heat]

except there's almost no other way to find it. Leak detector or dye are a
consumer's options. Detectors start pretty cheap. But the leak has to be
identified. That requires at least one can of R-134a.

I chased a minor leak for years. Stop leak did not work. 3rd party help
identified it as the evap core, which is a 2 hour job on 3rd gens.

 

[96RedRunner]

If Comp is engaging you may have just enough freon to satisfy low pressure switch and not cool.
Add shots of Freon with dye till it starts cooling or not, look for leak.
Is a possibility leak doesn't start till higher Op pressure is present.

 

[JohnMc]

None of the above. It doesn't turn off at all, when the AC is on. At least for the 5 minutes I ran it just now.

So the compressor is running the whole time? The very end of the compressor, the end facing forward, is turning? And it stops turning if you turn the A/C off?

If so, that points to some different sort of issue. With not enough R134a in the system it will run a short period of time, until it sucks the low pressure side down too far and the low pressure switch shuts it off. Then the high pressure side will slowly bleed back into the low pressure side and the compressor will briefly turn on again. If it's staying on, that's not happening, the low side pressure is staying high enough.

If the expansion valve is stuck shut, it will move enough of the R134a from the low side to the high side that either the low pressure switch on the low side turns it off, or the over pressure switch on the high side will turn it off. Since it's staying on, that's not happening.

So if it runs constantly and doesn't make cool air, here are a few options:
1) Failed expansion valve. These have (afaik) variable expansion valves, which work better over a larger range of cooling. I know they can fail shut, I'm not sure if they can fail open, or at least so far open they don't meaningfully cool. But it's a possibility, the compressor is pumping R134a around, but it's not getting enough of a pressure drop at the expansion valve to evaporate/boil, so no cooling? Feel the two lines going into the firewall on the passenger side, there's a smaller one and a bigger one. Are they different temps?
2) The evaporator inside the HVAC system has leaves piled up on it and is completely blocking airflow. So it gets cold, but you don't get cold air, the fan's just blowing air around from elsewhere.
3) The compressor is just completely worn out/damaged internally and while it's turning, it's not actually making enough pressure to do anything. The R134a needs enough oil mixed into it to keep it lubricated, without enough oil it will chew itself up.

I think you need to get some pressure readings at this point. A cheap Autozone refill 'kit' will have a low pressure side gauge, that's at least some information on what's happening pressure wise. Check the pressure with the system off and 'at rest' (it hasn't been running for a while). Then start it up and turn on the A/C and see what the low side pressure does. Goes down? How much? Turn the engine off and see how quickly the low pressure goes back up (assuming it went down with it running).

 

[Previologist]

So the compressor is running the whole time? The very end of the compressor, the end facing forward, is turning? And it stops turning if you turn the A/C off?

Yes. That's just running it 5 minutes or so, from a cold startup. Maybe I didn't run it long enough to shut down.

I could not pin down the source, but every now and then I heard a faint tic, as if something (maybe) was trying to turn on or off, but I am by no means convinced that's what it was. It didn't seem to be coming from the compressor.

If so, that points to some different sort of issue. With not enough R134a in the system it will run a short period of time, until it sucks the low pressure side down too far and the low pressure switch shuts it off. Then the high pressure side will slowly bleed back into the low pressure side and the compressor will briefly turn on again. If it's staying on, that's not happening, the low side pressure is staying high enough.

If the expansion valve is stuck shut, it will move enough of the R134a from the low side to the high side that either the low pressure switch on the low side turns it off, or the over pressure switch on the high side will turn it off. Since it's staying on, that's not happening.

So if it runs constantly and doesn't make cool air, here are a few options:
1) Failed expansion valve. These have (afaik) variable expansion valves, which work better over a larger range of cooling. I know they can fail shut, I'm not sure if they can fail open, or at least so far open they don't meaningfully cool. But it's a possibility, the compressor is pumping R134a around, but it's not getting enough of a pressure drop at the expansion valve to evaporate/boil, so no cooling? Feel the two lines going into the firewall on the passenger side, there's a smaller one and a bigger one. Are they different temps?
2) The evaporator inside the HVAC system has leaves piled up on it and is completely blocking airflow. So it gets cold, but you don't get cold air, the fan's just blowing air around from elsewhere.
3) The compressor is just completely worn out/damaged internally and while it's turning, it's not actually making enough pressure to do anything. The R134a needs enough oil mixed into it to keep it lubricated, without enough oil it will chew itself up.

I think you need to get some pressure readings at this point. A cheap Autozone refill 'kit' will have a low pressure side gauge, that's at least some information on what's happening pressure wise. Check the pressure with the system off and 'at rest' (it hasn't been running for a while). Then start it up and turn on the A/C and see what the low side pressure does. Goes down? How much? Turn the engine off and see how quickly the low pressure goes back up (assuming it went down with it running).

Will take a look. I have a gauge.

 

[Previologist]

Feel the two lines going into the firewall on the passenger side, there's a smaller one and a bigger one. Are they different temps? .

Didn't check pressure yet (shoulda done that first) but the obvious Low pressure (thicker) line was definitely not as cold as the small line after it ran for 10-15 minutes, and the compressor did not shut off. Wasn't a big temp difference, but it was there.

I traced the ticking sound to the plastic tips of my hoodie drawstrings as I moved and they tapped the fender or grilll. :brick:

 

[TheDurk]

I assume you still have Freon in there? If so, I would open the schrader valve and let whatever is left in there out. I'd replace it with R134a that has a self-sealer and wait to see what happens... but that's me.

No. Just no. Aside from the bad environmental effects of just venting refrigerant, you need to pull a vacuum to have any hope of decent performance out of the rig. Harbor Freight has a decent pump for a good price. Mine has paid for itself several times over.

Further, playing with AC without a set of gauges (both high and low side with fill tube) is really shooting in the dark. HF has those, too. For the occasional user like me, the HF stuff has proven to be perfectly adequate, so spare me the "Chinese junk" comments....

I had a slow leak that just needed a top off every spring, until it didn't. I needed a leak detector to diagnose the evaporator as the culprit (Tiff has a cheap one.) It was ridiculously corroded after twenty-plus years of service, so I suspect most original evaps are hanging on by a thread. It was a really simple job compared to the BMW and the Hyundai I have also done, which required removal of the entire dash. Brutal...I did everything aft of the firewall, i.e. evap, expansion valve, and all the o-rings, and the thing works like new and has been tight as a drum for four years.

 

[Previologist]

I think you need to get some pressure readings at this point. A cheap Autozone refill 'kit' will have a low pressure side gauge, that's at least some information on what's happening pressure wise. Check the pressure with the system off and 'at rest' (it hasn't been running for a while). Then start it up and turn on the A/C and see what the low side pressure does. Goes down? How much? Turn the engine off and see how quickly the low pressure goes back up (assuming it went down with it running).

I checked the pressure with vehicle cold and off. Tested to 52 psi or so, which shows up in the yellow range on the gauge. Turned the truck and AC on and it dropped to zero immediately. Decided I probably shouldn't run it that way so I went for a steamy drive with no ac.

I await the diagnosis.

 

[phattyduck]

I checked the pressure with vehicle cold and off. Tested to 52 psi or so, which shows up in the yellow range on the gauge. Turned the truck and AC on and it dropped to zero immediately. Decided I probably shouldn't run it that way so I went for a steamy drive with no ac.

I await the diagnosis.

Maybe a clog in one of the orifices then? That's an interesting one. Sounds like it is time for a professional to at least do a diagnostic on it.

-Charlie

 

[Previologist]

I don't know how accurate these cheap gauges are. I tested again and got the same results though. Slightly in the yellow (slightly overfull) engine cold and off, no change when engine turned on and ac still off, drops to zero when I turn the ac on.

Could being slightly overfilled (if indeed it really is) be closing something off?

 

[Previologist]

Google says overfilling can lead to poor cooling...but I didn't have time to discover why...

 

[Previologist]

Check the pressure with the system off and 'at rest' (it hasn't been running for a while). Then start it up and turn on the A/C and see what the low side pressure does. Goes down? How much? Turn the engine off and see how quickly the low pressure goes back up (assuming it went down with it running).

Forgot to do the last part of the test. The pressure goes back up immediately when I turn the ac off.

 

[Previologist]

I decided that having a high reading with the system off is perfectly normal, because the sides equalize with the system off. That indicated to me that there was still enough pressure in the high side to bump the low side up when turned off. Based on this possibly correct and possibly faulty reasoning I decided to add some 134a. It pretty quickly bumped up from zero to normal pressure when I added it, with engine running (and ac on of course). Looked like it might drop low again as if leaking, but I think that was just some equalizing going on because then it stayed steady. After a few minutes the compressor started a horrible screeching and I figured I was ruining it, so I turned the ac off, but at that time it was blowing cold air. Then I turned it back on and, it howled some more, and I cycled it off and on a few more times and it stopped howling.

So my hillbilly reasoning thinks the compressor was working harder now that it is under pressure and just needed to get some oil circulating to soothe it.

I might have broke it but it seems to be holding pressure and seems to be working quietly and blowing cold, for now.

 

[phattyduck]

Screeching could also be a loose and/or old belt.

-Charlie

 

[Previologist]

Screeching could also be a loose and/or old belt.

-Charlie

No belt noise with ac off, and brand new belts last year.

I've traced it to the compressor, when it screeches the compressor front (clutch plate?) slows way down. So clutch (or plate) bearing maybe?