I thought about this on the way into work this afternoon. I can't recall whether the 560 has a single relay for the heaters or a separate relay front and rear. If dual relays, the front could be acting up. No access to the manuals from the office so I can't cut sign for you.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.