These purple caps on my AC condenser are rattling. They are stamped NOVENT. They just spin when I turn them. How do I tighten them to make them stop rattling?

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Those are tamper resistant locking caps to protect against misuse or leaks of refrigerant. There is a threaded brass fitting inside that is tightened with a special "key" which you or your AC guy would have. The type of refrigerant is also stamped on the fitting. If the spinning of the outer ring bothers you so much, wrap it with some electrical tape extending it on to the valve.

  • I don't know how common this is, but my tinbanger left the special key behind an access panel. – Aloysius Defenestrate Jun 5 at 14:29
  • Well, using the key to let refrigerant out wouldn't really help OP. The valuable info here is that they are a security lock not a safety valve, so there's no safety issue with just taping them down. – Harper - Reinstate Monica Jun 6 at 6:39

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