what is a black thing/device?

来源: 于 2024-10-20 20:29:55 [旧帖] [给我悄悄话] 本文已被阅读：次

How long did it take you? 

If possible I would like to practice more on HVAC repair especially heater. Budget $500 per house per year. If HVAC life is extended by one year, it is saving of $500 - repair cost.