I'm trying to sort out my intermittent A/C issues. On occasion the compressor doesn't kick on when I turn on the A/C. By toggling it on and off a few times it always seems to work, eventually. I don't suspect the relay, as I have validated its clicking and working even when the compressor isn't turning on. I have a set of gauges but need to know the spec for the high side reading (Max/min) so I can determine if I am low or high on refrigerant.

 

just because the relay is clicking doesn't mean its allowing current to travel thru it and onto the compressor clutch coil. try swapping the relay with another just like it for test purposes. make sure to put it back if you find a/c relay is bad.

 

Most cars including ours run about 40-55psi for the Low Side, and 180-200psi on the High Side.

Not always common, but sometimes cars need to be relieved of a little pressure on the Low Side. For those with "correct Low side PSI" sometimes alot of that is air, and not enough Freon. Pressure needs to be relieved aka just pressing the valve, and exhausted very carefully and refilling with freon. This is why it works sometimes with people who completely vacuum out their system, and add freon- almost the same principal.

Also sometimes compressors are oil starved, most places sell half oil/half freon can mixtures.

 

Good tip. I swapped it with a similar relay under there and noticed no change in behavior.

 

Thanks for the input. A shop is who recharged the AC system completely, as I changed the condenser and swapped the motor, keeping the same compressor. So I don't expect there to be any air in the system, and the oil should be correct. Is that 180-200 number the pressure with the compressor kicked on? And how much fluctuation should be accounted for as it relates to ambient temp?

 

No problem! Yes, those are compressor running numbers around 80 degrees. For around 90-100 degrees, High Pressure can get upwards of 250-300. I know the SC and IS take around 14-16oz or 1.2lbs of freon, so ours is probably similar. Should be a yellow sticker under our hoods that say. Good luck, Ya'acov

 

Yes folks...
Pressures are directly related to the outside air and humility






.

 

Thanks, fellers. Good stuff! I'll try to get my butt out and test the pressure and report back on results.

 

So update. I got around to checking the pressure tonight. The garage was 80 degrees based on the thermometer in the garage, 77 based on the car's dash readout. Humidity around 80% based on weather check at the time.

Here's the reading on the gauge. The A/C did not cycle off the entire time I waited on it (about 5 minutes). Not sure if that's relevant or not.

Based on the charts above, I'm either officially "low" or right on the border of being low. Any thoughts as to how sensitive the switch is related to the AC cutoff in terms of pressure? I'm wondering if the switch is set to kick the compressor off right at the low mark or if it's a more significant difference, like 50% of operating pressure, etc.



Any thoughts / inputs would be appreciated.

Unrelated (I think) my ambient temp readout in the car has been erratic lately. It will swing massively, mostly in the morning when starting it for the first time, for about 15 - 20 minutes, fluctuating from actual ambient all the way into the negatives. I'm assuming it's the sensor that's up next to the high pressure valve. Is this right?

 

Your static pressure should be around 80psi, that is when both sides equalize.
Other than hooking up a machine that evacuates, weights and adds the proper amount of refrigerant ( Our GS's take 19.4-22.9 ounces of 134a refrigerant.) I don't know to tell that you have enough.

I would leave the gauges hooked up overnight and see if you are at 80psi on both sides.

good luck

 

The shop that out the freon in used the weight method to do so. I've already removed the gauges. Would hooking them up in the morning before starting the car get me the same result as leaving them hooked up overnight?

 

Yes you're low. You need to take your car to some place with a recovery machine. They will recover the refrigerant, see how much was recovered (will probably be lower than the 1.43 it should have). Vacuum the system, then inject about an oz of dye oil via the machine and charge your system back up with the 1.43 lbs of 134a. Then you'll drive around, cool air blasting, until it starts quick cycling again. At this point you wanna take it back to the shop that had the recovery machine and they'll dye check it for you and discover a magical leak. Or of course you could try all that on your own. Then you'll decide wether or not it's worth fixing (possibly your compressor leaking). The reason I say it's possibly your compressor leaking is because mine did on my 01 GS300. But hey you might get lucky, could just be a hose or something. Good luck!

 

They put dye in it when they charged it. Initially it leaked (well they claimed it wouldn't hold a charge, so I asked they tell me where it was leaking from) and so they changed the gaskets and put refrigerant with the die in it at the recommended weight via a machine. They then searched and could find no leaks. But the A/C wasn't kicking on. They asked me if I wanted them to trouble shoot it. I told them no, I would do so. I went home and jumped the clutch to kick on the ac. Thereafter it has worked (for the most part). I've seen no change in behavior. That was back in March/April.

So so at this point should I just consider adding some refrigerant and then monitoring over time?

Does anyone know the actual pressure point at which the compressor will kick off to avoid damage? I assume this is a pressure at non-operating levels which would be much lower than what I'd see with the compressor running.

 

I checked pressure this morning and high side was about 100 and low side was around 90. Since I had the gauges on, I went ahead and started it up and let it idle for about 10 minutes. The pressure on the high side stayed around 175 and low side around 26. I took a video of the process. I'll try to get it uploaded later today and post a link so you knowledgeable folks can tell me if it means anything. To me it's confusing, because temps were about the same this morning in the garage - about 81, but the pressures seemed a little bit more in line with spec than yesterday.

 

What "gaskets" did they change? The schrader valves? If you've already got dye in the system, get a UV light, park your car in the dark garage and look over all the components of your ac system; compressor,condenser, drier, suction, discharge(most likely to leak), and liquid lines. If you don't see any dye there look in the drain tube with your light (on passenger side fire wall). I don't think our cars are known for evaporator leaks but you never know until you look.

Your compressor will cycle when the low side pressure gets down to about 10-15 psi while it's running. You can simulate this by increasing your rpm to about 1500-2000 rpm while watching your ac gauges(since you keep asking). Static pressures are not very useful as air in your system can give a false static reading.