98 V70 It's SPRING Time for A/C Questions!

[rmmagow]

I want to "top-off" the charge on my A/C. It works, nothing's broken but I'd like to be sure it is properly filled with R134a. So, charge cans with the gauge commonly available at AutoZone et al is OK to use? Basically charge according to what it says on the chart? I hate fixing things that aren't broken but would rather be a little over cautious on the A/C system. Evap is good and cabin filter is in place and functional.
Thanks

[rspi]

If it is not cycling a lot, I would leave it until it does. Over servicing can worsen leaks.

[rmmagow]

Thanks Robert. Rough guideline, say 70 degrees outside, full on, what could one expect for cycling? Mine does cut out occasionally at near 100 degree temps but I'm pretty confident that is the bread-clip fix issue. I'll be putting that "mod" in place real soon before it gets hot here.

[jimmy57]

ALL A/C CHECKS ARE DONE WITH ENGINE RUNNING AT HIGH IDLE.

There, I said it.
Get it to 1200-1500 rpm using a stick on accel pedal and adjusting seat.
Set fan to next to highest speed
Recirculated air selection
Closed windows
Thermometer in center vent
If the discharge air temp gets below 50F and it begins to cycle compressor with on period no less than 8 seconds and off no less than 6 seconds then do not touch it. If it is hot weather then the cycling may not occur for a long time and not at all if car is in bright sunlight and ambient temp is over upper 80"s. If it doesn't cycle on a hot day then turn fan to lowest speed and see if it cycles. If the suction line back to compressor is not in the 30's after it runs for a few minutes then it needs refrigerant. Only add small incremental amounts and check after 2 minutes to see if the suction line is getting colder. If it doesn't STOP! the system may have other problems and needs high and low side gauge monitoring to see what else may be wrong.
CCOT refrigerant control a/c systems can't be charged by pressure accurately. Temp, engine speed, humidity, fan speed, heat content of the car, and ambient temp all will vary high side and low side pressure. Expansion valve systems with fixed displacement compressors have stable low side and the charging pressure method works sort of OK on those.
If it is a vehicle with variable displacement compressor then that throws complications in the mix for gauge monitoring partial charging.
All short 6 cylinder (3.2 and the 2008 up 3.0 Turbo) use VD compressors as does the P3 S60 5 cylinder. The new for 2015 4 cylinder uses VD compressor also.

[wheelsup]

If you want to do it right go to Harbor Freight armed with a 25% coupon and pick up their HVAC gauge set for around $45. Hook it up to the low pressure charge port and observe with your AC on. If the compressor doesn't cycle with increased engine RPMs due to low pressure cutout (hold throttle cable and increase RPMs while watching gauge) you don't need any refrigerant added.

IIRC the low pressure cutout switch is set to around 20 psi.

[rmmagow]

Thanks folks, thanks especially to wheelsup, you reminded me I have a nice new unused HVAC set in my garage someplace. Bought it 100 years ago for one of my cars then realized the car was an R12 car so I got a different set for that. On to the garage hunt