R-Pro › Field cases › Air conditioning
AC Relay Fault — Contact Wear / Coil Open
Likely causes
Check relay coil + contacts together
Check: Coil resistance = ∞ means open coil. Contact continuity = 0 Ω when on / ∞ when off. No click on activation = coil bad. Click but no output = contact wear. Burn marks/arc traces on contacts = overload or end of life.
What to do: Measure coil resistance. ∞ = coil bad → replace relay. Contact continuity = 0 Ω when active, ∞ when off. Burn/arc marks = contact wear. Some relays soldered to PCB = replace whole PCB. SSR (solid-state) = no contacts; replace with same load rating.
Relays are PCB-mounted = damage often means PCB replacement. Some relays can be soldered out and replaced (skilled tech). Solid-state relays (SSR) = no contacts, long life but lower load capacity.
All 565 cases work offline in R-Pro, with error codes for 62 brands and P-T data for 108 refrigerants.
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