Air con compressor cycling, 1994, 850 2.0L GLT

[StephenM]

143k miles, owned without issues for 5 years, except driver's side (UK) door stay fatigue.
I have read all the threads I could find on the site and have slightly different symptoms to those posted:
I have manual air con, set to max cooling the compressor kicks in and out every 3s, both on and off.
I checked the LP switch by bypassing it and the comp runs constantly.
I added 134a to 40, 50 and now 65 psi (as the threads say this will even itself out in the system, despite being high).
I bypassed the switch to circulate the 134a, got some cooling and pipe icing after the restriction before the evaporator.
Plugged in the LP switch lead and the compressor starts cycling at the same rate (3s on, 3s off) and the cooling gradually faded over 2 or 3 mins.

What next? I'll bet someone knows...and all answers welcome!

[Ozark Lee]

I added 134a to 40, 50 and now 65 psi (as the threads say this will even itself out in the system, despite being high).

Are those pressures with the compressor running or not running. If the compressor is not running at those pressures the charge is still to low. If those are the pressures with the compressor running they are way to high and you are overcharged.

With the compressor off I usually see pressures around 100 lbs or more depending on the ambient temperature. With the system running (compressor on) the pressures are in the 30 PSI range.


...Lee

[StephenM]

Those pressures are with the compressor off. I tried jumping the LP switch to make the comp run and checked the pressure - you were right, it was low.
The cans of 134A didn't have enough pressure to take the system pressure all the way to the required 30 ish, so I will go to a professional.

Thanks for the help - good site!

[MadeInJapan]

You have to add the gas with the car running. To help add the gas, I often put the cans in a bowl of warm to hot water...this helps them empty quicker anyway.