Even though your monovalve has no function except when in heating mode, it can affect the ac if it has failed.

The normal (unpowered) state of the monovalve is OPEN. A control voltage closes and opens the solenoid valve to regulate heat. A torn rubber diaphragm (common) will allow hot water to pass through the monovalve at all times and will overwhelm the ac. Similarly, a loss of control voltage at the monovalve connector will have the same effect.

You can measure the presence/absence of the control voltage at the connector and inspect the monovalve diaphragm very easily by disconnecting the connector, removing four screws and withdrawing the solenoid piston assembly. If needed, a new piston assembly is in the $30 range. Should take no longer than an easy 15 minute DIY.