A/C air conditioning

Ive got some A/C problems....

car 1: rapidly on/off alternating about every 5-10 seconds. Just had a refill.

car 2: Checked the coupling and it engages when power is applied (when its out of the car). But when its in the car it wont engage. System is empty as when I went for a refill, they emptied it again because it was not working.
Checked the sensor on the compressor itself and was fine.

I also cannot find checking procedures of the transistor/resistor that sits under the dashboard inside the blower housing.
Attachment 82387

Do we have a A/C controler / ecu, or is this the A/C unit in the dashboard itself?

Any other tips that I can check?

cycling the compressor on and off every 10s or so is normal for the unit when the ac cooling load isnt high.
The ecu will also use outside air if the outside temperature is at or near to the inside temperature.
There is a dual pressure switch built into the drier which is worth checking. also confirm what charge quantity was used.

Section 55 of the workshop manual covers the system in detail (afaik VR4 is the same as 6a1 non turbo cars automatic system)

Car 1: Its 35°C outside, and even hotter inside the car. So I dont think its normal its alternating on/off that frequent.
Als for checking the high/low pressure switch you need to have the filling machine attached. And I dont have that obviously. Any other ways of checking this?

Car 2: I did check continuity of the switch and in 2 other cars it had continuity when off, mine did not, so 1 switch is fried. I did short the plug and the clutch now engages. So ordered a new switch and will fill it up again.

the continuity might be because there was no charge. but its a good start!

might be cycling on high pressure (or low) on the first car if the charge quantity is wrong or something is blocked up (AC stop leak could cause this, as could kinked/pinched pipes, deteriorated hose, bad condensor, bad evaporator)

Im not an AC engineer so cannot advise much more, try following the flowcharts in section 55 on both cars and see where you can get :D

if the compressor clutch is not engaging when the compressor is in th car but you ca activate on the bench then i would suggest you have a problem with the clutch engagement signal from the cars loom.

i had a very similar issue and it turned out to be a broken wire in the loom as it went over the front valve cover the clutch wire is one of the three that goes down to the power steering pump and the A/C compressor. the wire had just got old and the insulation very brittle in the heat from the turbo and valve cover the wire had snapped at the crack in the insulation so sometimes it would work and sometimes not, then i had the compete wire failure and it was easy to trace by tacking the connector off the A?C pup and tracing the back past the valve cover to the main branch of the loom them cut the soft insulation there and measure resistance to the wire (tape up insulation cut afterwards) in the a/c plug and see if it connected. or you can take it right back to the fuse box and measure for resistance there with the A/C fuse pulled out and with the fuse put back in you should be able to measure the voltage at the a/c plug.