My A/C blows hot air for a moment then blow cold few minutes and then hot again and cold, eventually blow hot.

Refilled freon, replaced refrigerant pressure sensor, replace auxiliary water pump still blow hot air.

OBDI scanner still said "9304 M13 heating water circulation pump open circuit".

Is there auxiliary water pump (heating water circulation pump) relay or fuse?

Please advice.


God Bless,


Did you happen to ever figure out how to fix this issue?

I have a 2008 GL450 and have the same issue..



No, I have not. but I took the car to shop for other reason and told them the AC issues and they checked and adjust the freon pressure.

Basically it was too much freon. after that it worked for a moment ( 2 hours) then went back to same as before.

I guess I have to go to the repair shop.


good luck.


sorry i obviously didnt read your entire first post until now..

as i mentioned mine was just the wire connector.. maybe the wire is frayed or nicked?

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