AC Refill

[dunbar26]

My AC has not been working. Compressor not engaging at all. It’s been getting hot here lately and purchased an AC pressure gauge off Amazon. Today I went out and hooked it up. Read under 20 on the low port and around 50 on the high port. Both low so I decided to refill the refrigerant.

I pierced the can and set ac to high on the car. The low side pressure rose a bit then dropped very low once the compressor tried to engage. After a second or two the compressor failed to kick on and the pressure went back up. This kept happening over and over. Compressor off pressure is high compressor tries to start pressure drops.

My initial thought was the system is extremely low on refrigerant. So I kept adding refrigerant until the pressure (when compressor is off) got up around 55 and I got nervous about overfilling and decided to stop.

Is it normal for the pressure to fluctuate that much? Could the system just be extremely low? The compressor still would not stay running after adding (a little) refrigerant.

 

[Big Z]

Sounds to me like it's acting like a typical DIY refill with a nearly empty system.
When you have a nearly empty system, the compressor will cycle on and off rapidly because there isn't enough refrigerant to keep the low side PSI high enough. You need pressure on the low side to avoid starving the compressor & running it dry. If it's practically empty, the compressor will suck the low side pressure down very quick & open the pressure switch. It will not allow it to turn back on until the low side PSI builds pressure again.
When you 1st start your a/c on a hot day, the low side is equalized with the high side & probably resting in excess of 100psi. Low side PSI charging is done with the compressor engaged.

 

[dunbar26]

So low side PSI isn’t important when compressor is off?

 

[shucker1]

No sir.

System will equalize pressure on both sides with compressor off.

Just don't flip the can upside down during filling. You could "Slug" the compressor with liquid and be in for a "**** Show" with a busted compressor.

As an alternative locate the low side pressure switch (Usually on the accumulator) remove the electrical connector and jump it with a paperclip.

Makes the compressor stay on during filling.

I usually have windows down and A\C on high blower during filling. A thermometer in a dash vent helps to see whats going on.

I fill until a see sweat back on the low side line (Cold to the touch).

 

[shucker1]

Target high side pressure I find is usually 200 PSI to 225 PSI on a hot day.

 

[RickOTR]

Isn't jumping the LPS bad for the compressor? Had to replace receiver/drier, orifice tube (went with red instead of blue which was factory) and a few o-rings that were leaking. Put 2 oz of PAG46 oil in the receiver/drier manually but could not get the compressor to turn on.

 

[shucker1]

Isn't jumping the LPS bad for the compressor?

Your not doing it for long term usage, only for filling purposes.

The worst thing is to turn the fill can upside down during filling. Then you slugging the compressor with liquid.

Yes, running long term negative suction pressure on the compressor could damage it.

 

[ExplorerDuece]

I have question. How do i test if the clutch on the compressor is bad? Can a bad clutch still engage but not cause the system to cool the air enough?

 

[Big Z]

You could use an ohm setting on your multimeter & verify the coil has low (~2-5 ohms) resistance across it's 2 prongs. And also verify battery voltage to the plugin. And I think you may be able to carefully tap the hub face on these while it's running to see if it's an excessive air gap problem. Poor cooling is unlikely to be a clutch slipping problem if it is actually engaging (you could probably tell with a visual inspection)... at least for very long before it totally gives up.

 

[shucker1]

A slipping clutch will usually turn a rust color as the metal on the [2] surfaces wears away.

The heat gets so bad it also will melt the rubber damper.

Have you taken any pressure readings?

Would like to see High Side, Low Side and vent outlet temp with A\C set on max air.

 

[Davidm53]

Spent the $126 the other day on my AC. It was cooling but warmer temps at higher speeds.
Connected to a Snap On machine and was several ounces low on coolant.
Had that clutch growling noise for a couple years also.
Correct amount of Freon and Oil and working much better.
35 degrees.