No hot air from HVAC after warm up

[Cailein]

Just noticed here in upstate NY that our HVAC blows nothing but cold air after 30 minutes or more of driving. Seems like the AC is on but isn't. Temperature is set for well above 70 degrees. There was a time driving that warm/hot air was blowing, then shut off the vehicle, started up and cold air was again blowing. Anyone experience this and have thoughts? The dealer will be next, but would like to know what it may be. Thanks in advance for any responses.

 

[99WhiteC5Coupe]

Just noticed here in upstate NY that our HVAC blows nothing but cold air after 30 minutes or more of driving. Seems like the AC is on but isn't. Temperature is set for well above 70 degrees. There was a time driving that warm/hot air was blowing, then shut off the vehicle, started up and cold air was again blowing. Anyone experience this and have thoughts? The dealer will be next, but would like to know what it may be. Thanks in advance for any responses.

Including the make, model, year, trim and type of HVAC system would help others provide you with information.

Check your engine coolant level. If lt is low, an air pocket can cause low or no heat output.

 

[TDBDLB]

Yep, low coolant can definitely cause this condition.

 

[BigOleFordFan]

Yep, low coolant can definitely cause this condition.

As can a clogged or blocked heater core, which could possibly be resolved with a complete cooling system flush & fill, the full one where everything is drained, filled with a cleaning solution, then back-flushed under pressure to get all the grime & gunk out, then flushed a 2nd time with clean water to get all the cleaner out, then refilled with fresh coolant...

However, if the heater core has failed, it would need to be replaced, but the flushing may help and is certainly cheaper to do if it works...

 

[Cailein]

Thanks for the responses. Fluid was low and took a gallon of coolant. Heat is now working and will likely get the system flushed and checked for leaks.