I am making a very general inquiry to see if there are common problems which might cause this issue.

2008 CVPI which is completely stock. The HVAC system, to my knowledge is the same as installed from the factory. Went out for a 15 minute lunch and ran the car AC. No trouble, no odd noise. Inconsistent idle, but that's a work in progress repair. Shut the car off.

Came back out after work to find that the entire HVAC system no longer works. When engaged on the climate control, I can hear coolant flowing. Aside from the BJB blower relay, is there any other common problem which could cause this?
2008 White P71 | Former Millbrook, OH City Patrol Unit 15 | Yellow/Amber Visor Lighting For Roadside Utility And Freelance Security Work | One Deer Collision | My Brother's Personal Uber, I Guess