What could it mean when my ac compressor clicks on for about 3 seconds then off for 5 seconds? This will continue as long as ac is running at any fan setting. Also, ac is only mildly cold with pressure showing at 55-57 when on and down to around 23-25 when off.
Thanks!

Forgot to mention it's a 96.
Thanks

 

Your system is low on refrigerant. The low pressure switch will deactivate the clutch when the low side pressure drops below ~25psi.

 

Ditto. look at this and understand it:


Notice that 'low side' pressure which reflects the temp of air passing over your evap coil {heater box} stops increasing at 55.

That's why I recommend filling slowly.. bottle upright.. with AC on max, blower high, and windows closed till the cabin reaches 75 deg. Then your max low side pressure should be about 40 lbs and the vent temp about 55-58 deg when clutch on.
Once that happens, dont worry about switch being activated on low pressure, that's how it works.

If vent temp is under 60 deg in idle, system is full enough. Better a little low than overcharged, especially when outside temp is over 105. Check the high side chart on that.

Check the system capacity label. Never add more than total factory charge. I actually watched a guy dump two pounds into a 1.5 lb system.. 'because some worked good, more would be better'.

heh...

 

Aaaaahh I get it! I was worried that when the gauge was going up to 55 that meant I was already full but now it makes sense that reading needs to be constant... Put in about half a can for now and all is well!
Thanks guys, you RULE!

 

'MORE constant!'

Once you get the cabin temp where you want it.. like on freeway.. you slow the air passing over the evap by either turning blower down or changing blend door... the evap gets colder then the pressures WILL cycle the switch.

\This is subject to system limitations.

Note for everyone to remember:
The static {car not running} pressure in a refrigerant system says not a thing about how much refrigerant is in the system, it reflects the lowest temperature point where there is both liquid and vapor. As long as there is some liquid in the system. If there is no liquid refrigerant left, the pressure will no longer reflect the temperature.

Park the car in the sun for several hours.. measure the temp under the hood. Hook up the gauge to either side and see if the pressure read matches the temperature read. If so you still have some liquid in the system and rule of thumb dont have to evacuate it. If the pressure is lower than the temperature indicates, then you should evacuate the system before charging it.

This can also be used to find if the system has r 12 or 134 in it. There are some out there.. where guys converted without adding the new couplings.
But in a non-working system you would have to compare in-sun to in-shade temp/pressure to see which the pressure tracks.
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