CL65 Captain arrives at the aircraft to find APU fire detection Loop A deferred; and the squibs do not test. Maintenance finds that a circuit breaker pulled for fault identification has been left out and collared. With the circuit breaker reset the squibs test normal. The aircraft had flown for two days in this condition.

Narrative

We arrived at the airplane and noticed Fire Detection Loop A for the APU was deferred. I tested the squibs and noticed no squibs messages (1 and 2) for the APU where displayed. After multiple tests; I queried the First Officer for system knowledge. Would the squibs not test if a loop is deferred? We discussed it and agreed they are separate systems and should test correctly with an advisory message. We called Maintenance Control; whom called out a Mechanic. We explain the problem we were having. He did multiple test; including depowering the aircraft. After further review of the MEL for APU Loop A; we found (I believe) circuit breaker 1R5 pulled and collared. Although the MEL does state to open 1R5 and 1R6 to find the faulty loop; it does instruct the Mechanic to close both circuit breakers. The logbook showed two full days with this deferral. If there would have been an APU fire; I do not believe squib 1 would have worked. Maintenance closed the breaker; the APU test for the squibs worked and they signed off the book.