Need help with Suburban heater/blower fan

[Danebo]

I have a 1994 Suburban 2500 4x4. I'm having a problem heater fan. It is on full blast and I can't shut it off or slow it down. The off button isn't working nor is the fan/blower control. All other controls with the main control unit seem to be working fine. Is it possible that 2 relays could go out at the same time or does the whole unit need replacing?
Any answers would be helpful.

Thanks,
Danebo