Ford Focus 2000 freon refill

If your A/C compressor clutch is binding or seized, - the extra load will slow down the engine as everything runs on 1 belt on this car - check your Freon level and refill or replace the clutch/compressor

Try a jump wire across the low pressure switch on the receiver dryer,if
the clutch engages and stays on check for cold air.
if no cold air disconnect jump wire and regas.

Make sure your blend door is closing all the way and that the actuator actually works.

Sounds like you are low on Freon. The engine has a separate RPM control which is used to increase the speed anticipating the A/C clutch to engage. When the A/C clutch does not engage, the engine overspeeds. The system then slows down and you get the variation you describe.

Service the A/C. If you try to do it yourself you will be alright if there is still a little Freon in the pipes. But if you do not have any pressure, th leak will need to be found and fixed. Then borrow a big Vacuum pump and evacuate the system. Best performance is a pressure between the high and low limit switch cutouts.

I assume it's because your clutch is engaging and disengaging. Could be from a loose electrical plug to your compressor coil on the compressor. It could be a loose plug to the pressure sensor or a bad pressure sensor because that sensor will shut it off if the car is low on Freon causing low pressure in the system. Could be low on Freon so it's on the edge of having enough pressure to turn it on and then shuts it down again because it dips below the pressure threshold when the compressor kicks in. Could be a bad compressor coil that engages the clutch. Maybe a loose connector to the AC Button in the car or the AC Button is intermittent. Could be an intermittent relay engaging the compressor clutch. That's a good list of what all could cause it and if you end up needing to replace the compressor, I made a video on how I did it.

Check to see if A/C clutch is engaging. If it is not engaging, the compressor is not starting which will prevent the freon from being sucked into the system.

Look at the front of the ac compressor and have someone turn on the ac from inside the car. The front of the pulley(clutch) will spin when turned on.

If it does not spin, the low pressure switch (LPS) is not satisfied. Meaning there is not enough freon in the system to operate the system. Probably means a significant leak.

The LPS can be jumpered to cause the compressor to run (clutch to engaged) which will draw the freon in the system.

The LPS is usually a two wire sensor on the suction of the compressor. (between evaporator and compressor) Unplug the sensor and install a jumper, this will engage the clutch.

However, if it is empty the leak must be repaired.

The capacity of the ac system will be on a label under the hood, do not overfill. Probably about 2 lbs. Local parts stores (Auto Zone and Advance) will have freon with stop leak. This may help the leak. They also make a freon with a UV dye. I always add a single can with dye so that if stop leak does not work I can find the leak in the future.

The system should be filled until suction pressure is about 36 psi.

since this is a standard and you need to engage the clutch which basically shifts you into neutral to shift gears, this ALMOST sounds like the idle air control valve.

Check the a/c pump on the engine, it hac a magnetic clutch on the front and will not engage unless there is enough pressure,with the a/c on, fan blowing and engine running look at the front of the pump, it all should be spinning, if the hub is static then probably the gas is low. KEEP fingers, hands and clothing out of belt (a lot of us have done that, it hurts at least)

If all the freon is in the system and there are no leaks, then then next point to check will be the electrically driven clutch inside the pulley that drives the A/C compressor. The clutch itself is what turns the A/C on or off. So if the clutch is OK, then probably the switch that drives the clutch is defective.

if compressor clutch dont kick in .it has a open in clutch coil.