Engine stalls when A/C compressor engages

Its probably the ac compressor clutch pulley is seized and when engage the ac system it most likely stops the belt and seizes the engine causing it to stall until the ac system is disengages. But if the compressor is okay sometimes when you disconnect the battery the engine must go through twenty five running cycles to reboot the computer. Or your throttle bore needs service. Be sure your battery connections are tight and clean. You may even need a throttle body service to help strengthen the idle, see the guide below

https://www.2carpros.com/articles/throttle-actuator-service

Please run down this guide and report back.

Might want to try this.found bulletin #1878920. Engine stalls when air conditioning is turned on at idle - keywords HVAC rough condition CJ2 CJ3 surge. Engine may stall with the air-conditioner on and or while adding additional loads to the engine at idle. An example of an addition load would be turning the steering wheel left or right with the air-conditioning on. This type of stall usually occurs during idle or slow parking lot maneuvers. This concern may not set any diagnostic trouble codes.

Clean the throttle body bore and the throttle valve plate using a clean shop towel with GM top engine cleaner, GM P/N 1052626 (Canadian P/N 993026) or AC-Delco Carburetor Tune-Up Conditioner, P/N X66-P, or an equivalent product.

Here is a guide to help you see what I am talking about:

https://www.2carpros.com/articles/throttle-actuator-service

Please let us know what happens.

Cheers

When you turn on the A/C, the A/C compressor kicks in. This puts a small load on the engine. The rpm's should go down a little. However, when you disconnected the battery, all the sensors that compensate for this load- lost power. The IAC valve can very easily cause the problem you describe and may need to be reset. To do this follow the following:
1: disconnect and remove the IAC valve.
2: measure the distance from the tip of the pintle to the mounting flange. It should be 1 and 1/8 of an inch, if not push the pintle in so it is.
3: re-install the valve.
4: cycle the key on for ten seconds and off for ten seconds. This resets the valve.
5: Start the engine (do not press the gas) and let it idle for five minutes, then shut it off for thirty seconds. Then start the engine again and drive around for a while and test the A/C. During all these steps do not turn on the A/C until driving around during step 5. Let me know how you make out.

https://www.2carpros.com/articles/stall-at-idle

and

https://www.2carpros.com/articles/how-to-replace-an-idle-speed-control-motor-iac

By the way: the IAC valve is the idle air control valve. This valve controls the amount of air allowed to bypass the throttle plate when the throttle plate is closed or at an idle position not necessarily at engine idle, it is at throttle position idle.