Intermittent AC, no clutch engagement, odd woosh sound at idle...overcharged?

[lobo411]

OK, total rewrite:

1996 Explorer 4.0 175k. AC worked fine until I accidentally left a can of R-134a attached to the gauge set with the valve open and engine off for 10 mins. This may have overcharged the system. All pressure readings are low-side. Apparently, the kit Amazon sent me contained a defective high-side adapter.

Symptoms: After 5 mins of running great, the clutch disengages and all I get is warm air. It might come back after 5-10 mins or maybe not.

System seemed to be running at odd low side pressures, ranging from 26 psi to 50 psi at the same ambient temp (90 degrees F) and in the same 10 min window.

When the system stopped running, the car exhibted odd symptoms: a "woosh" sound coming from the air intake box, which might be the IAC valve opening wider in anticipation of clutch engagement), a brief lag in the idle, and no AC.

I'm not sure what's going on:

* I tapped the high pressure switch when the system was off, and the clutch engaged

* I discharged some refrigerant and got the system to stop misbehaving altogether. It now runs at 37 psi at 90 degrees w/o wooshing, shutting off, or anything. However, it's also not as cool as it was before.

Any ideas? I'll have to road test it some more to see if I fixed the problem or just masked the symptoms. Pity I don't have a working high-side adapter.

Video 1, showing wooshing sound and no clutch engagement


Video 2, showing the effects of my tapping the high pressure switch. All readings at 90 degrees ambient temp.



The gauge shows the low side pressure. In the first minute, the system gets down to 35 psi, it rises to 47, and then it drops to 44. The clutch was engaged until 0:56.

At 0:56 I tapped the switch, and the clutch disengaged. At 1:13 I tapped the switch again, and the clutch disengaged. At 1:32 I tapped the switch again, and the clutch disengaged.

 

[david4451]

If engine was off with can attached you may have pushed fluid back into can and your system is actually under charged.
When engine is off high and low sides balance, thus increasing low side pressue.

 

[lobo411]

If engine was off with can attached you may have pushed fluid back into can and your system is actually under charged.
When engine is off high and low sides balance, thus increasing low side pressue.

Good point! Anyway, discharging some 134a didn't fix the problem, so I added more 134a just now. It's ranging from 20-40 psi on the low side at 80 degrees. The clutch is still disengaging and making the "woosh" sound as heard in the video. Really weird.

 

[david4451]

With ac on and blower on max at 600 rpm my Sport Trac reads 42 psi, constant. Outside temp 80 degrees F. The compressor stays engaged.
If your compressor is switching on and off in above conditions I'd say you are still short of charge, or you have a leak not allowing full charge.
I don't know what the 'woosh' is, do the cans your using come with lubricant? If not that may be why.
Just noticed that 'woosh' isn't your compressor as it's not engaged on video.

 

[lobo411]

With ac on and blower on max at 600 rpm my Sport Trac reads 42 psi, constant. Outside temp 80 degrees F. The compressor stays engaged.
If your compressor is switching on and off in above conditions I'd say you are still short of charge, or you have a leak not allowing full charge.
I don't know what the 'woosh' is, do the cans your using come with lubricant? If not that may be why.
Just noticed that 'woosh' isn't your compressor as it's not engaged on video.

Ya, the "woosh" sound is loudest at the air intake (I have a cold air intake) and it's immediately followed by a slight increase in idle speed, then a decrease/shudder. The behavior stops entirely when the a/c is switched off or the clutch successfully engages.

My guess is that the a/c is supposed to be on/clutch engaged, so the computer revs the idle to compensate. Then for whatever reason, since the clutch isn't engaged, the idle surges too much and the computer cuts back to compensate. Weird.

 

[lobo411]

With ac on and blower on max at 600 rpm my Sport Trac reads 42 psi, constant. Outside temp 80 degrees F. The compressor stays engaged.
If your compressor is switching on and off in above conditions I'd say you are still short of charge, or you have a leak not allowing full charge.
I don't know what the 'woosh' is, do the cans your using come with lubricant? If not that may be why.
Just noticed that 'woosh' isn't your compressor as it's not engaged on video.

You were right about the system actually being low rather than overcharged. I still am not 100% sure what's going on, but here's what happened since my last post:

I thought about it and realized that I could not have overcharged the system. I was simply confused about how the gauge set works. When I left the can connected for 10 mins, I left the can tap open but the gauge valve closed, so nothing at all was moving between the a/c system and the can.

Then when I vented some R134a, I actually made things worse by *undercharging* the system.

I added more R134a and it seems to be working better, but we'll see. Right now it does this:

Ambient conditions: temp 91 F, humidity 22%

First a/c startup ---> 5/10 mins. Ice cold air, condensation/frost on the low side pipes, low side pressure 20-25 psi.

Clicked off, got the weird "woosh" thing, and then it clicked back on again. Low side pressure 35-40 psi, a little condensation on the low side pipes, cool air but not as cold as before. The clutch stayed on until I decided to stop 5-10 mins later.

 

[david4451]

The pressure switch on low side on drier is supposed to close and kick in compressor at 30 psi. Below that it should not kick in compressor so your reading of 20 to 25 psi should not be engaging the compressor!
The woosh is probably r134a vaporising through the drier/evaporator. Suggesting lack of r134a.
If you have a leak this is probably why your having various readings, or your still under charged.
My ST did things like yours and I'd charge the system and on that day all seemed OK. Three or four days later the compressor was kicking in and out. There were no signs of leaks, but I recharged again and went back to normal. I've a 30 lb container of r134a so recharging didn't cause a headache, except for ac not working properly.
To cut a long story short, I had a pinhole leak in my evaporator which I replaced after much trial and error with new compressor etc etc. I live in Philippines (British) and do all my own maintenance and this took me ages to solve, mainly due to having to ship parts from USA.

 

[lobo411]

It seems to have a good enough charge to stay on, and the system is still acting weird--the compressor is cutting out at random low-side pressures that are well above the cut-off level (it cuts out at random points from 35-70 psi). When the system does run, it runs great--ice cold.

When it's doing the *WOOSH* thing, there is no power to the a/c clutch (confirmed w/ voltmeter). So the clutch seems to be working fine.

The only thing that has been consistent is that I can tap the low side switch with a rock and get the compressor to come back on. I'm going to take a chance and replace it, since it's only $16.

 

[J_C]

Ya, the "woosh" sound is loudest at the air intake (I have a cold air intake) and it's immediately followed by a slight increase in idle speed, then a decrease/shudder. The behavior stops entirely when the a/c is switched off or the clutch successfully engages.

My guess is that the a/c is supposed to be on/clutch engaged, so the computer revs the idle to compensate. Then for whatever reason, since the clutch isn't engaged, the idle surges too much and the computer cuts back to compensate. Weird.

One thing I noticed when my IAC valve needed cleaning was an interaction with A/C compressor cycling, including a dip/stutter in idle speed, though at the time I didn't have any A/C issues.

 

[david4451]

That's a good point JC, especially if engine not at operating temperature.
Also to take low pressure switch out of loop, you remove switch and use paper clip in its contacts, making it permanently on while checking effect on AC operation.

 

[lobo411]

I just hate dealing with electrical stuff, so I'd rather replace things than short-circuit them even though I know that it's perfectly safe to do so. Anyway, the low pressure switch came in this afternoon and I replaced it. A spurt of green-colored stuff came out when I pulled the switch, which I assume is a/c oil. I kinda wonder if maybe a bunch of oil accumulated in the schrader valve and intermittently blocked the switch from properly detecting the pressure. Anyway, the new switch is on and so far so good...I ran it about 10 mins and the clutch stayed on the whole time. Hopefully, that fixes the issue!

The charge may or may not be out of whack at this point, since I messed with it so much. It runs at 45 psi low side at 95 degrees air temp, 10% humidity (all the hot, desert air blowing in...ugh). That seems a little high to me, but I'm leaving well enough alone for now. Before I started messing with it, it ran at about 25 or 30 psi at 85 degrees.

 

[lobo411]

Problem solved...it was the low side switch. Works perfectly now. Thanks for the replies!