avoid buying a whole new PC board. The old relay was 24 vdc and is twice as big as the new one so the new one has a much smaller armature so it does not run well on unfiltered DC like the old one did. The old, large relay armature must have provided 'mechanical filtering'. New PC board with original relay = $220, new relay $11. The original Airpax relay has been discontinued. Adding an RC filter to run the new relay: 1 hour of assembly & debug, 1ea. 60v capacitor, 1 ea. resistor.