I have my heater box out to replace heater core. Should I replace the actuators or just test them to see if they are functioning. Taking the box out again anytime soon is not a project that I want to mess with.

 

I wouldn't replace them unless they were bad. I've had my heater box out half a dozen times over the years to replace blown heater cores and never replaced the actuators, AC and heat still work fine.

FYI, don't re-install that one nut behind the fender well. The box will hold onto the firewall just fine without that one hard to reach fastener.

 

^^^THIS^^^

You can test the actuators with a hand operated vacuum pump, but as long as they work you should be fine.

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