Originally Posted by Beejmac
I guess I don,t know how to test a relay, is it a visual inspection?
Are the relays so cheap I should just replace?
The Starcool relays are are riveted to the Starcool panel, not a huge deal, and you would have to be careful in making sure the wires got back in same place.
The Common SPDT Relay.
To test you can use a ohm meter to check the continuity between first The NC (87a) throw and Pole(30) connection, There is no power needed for that connection to be present. The NO(87) throw to Pole(30) connection should be open. You can apply power to the coil, generally tab (85) will be power and (86) will be ground, although the coil won't care. The polarity really becomes important if the relay has diode protection.
When power and ground are provided you can usually here a click as the trow moves. Now with a ohm meter check NO(87) to Pole(30), it should now show continuity. The NC(87a) connection to Pole(30) will now show open.
This is all done on the bench with the relay out of the circuit.With careful analysis of the circuit you can also validate if the relay is working in circuit. Unfortunately it can be difficult to reach some of the output pins.
Here are the effects of the first switch, this is tied via a SPST switch from ground to ping 86 of relay (5). On older systems relay 5 and the switch may not be present as it was added in June of 2000. This allows power from the 20 amp fuse (12 blower Motor) via terminal block (pos 8) to the relay(5) Pole (30) connection and (85) to provide power. The switch normally positioned left side of drivers head will supply ground to the coil (86) and power will go trough the relay via NO (87) throw, and proceed to the input of the blower switch. It doesn't matter if the power switch is on or off it has no power
The next driving item will be the starcool blower switch. It provides a 12 volt output when it is in low,medium, or high. This will go through the terminal block (pos 5) to relay 2 power in (85). Now we have power coming from 20 amp fuse (12 volt condenser) to pin (30) of relay 2, now with power supplied to the relay pin (87) now has power. There are two paths (wires) for this output. Ones goes back to the fuse block 5 amp fuse (120 volt comp motor), the other goes yo the 12 volt condenser motor. The 5 amp fuse output goes to the pole (30) connection of both relay 3 and 4. In the case of relay 3, we have the NC (87A) connection wired via the terminal block (pos -4) and to the thermostat.
From this point we have two choices, running on shore power or assisting the 12 volt system while driving. If the thermostat temperature criteria is met the connection will continue to the terminal block(pos-3) to the power(85) pin of relay 4. As we already have 12 volts on the Pole (30) connection the 12 volts now goes out the NO -throw (87). This will split and supply power to via the terminal strip (position 1) to a relay for the 120 volt input, obviously the 120 volt breakers must be on. It also provides power for a 12 solenoid valve that redirects the flow of Freon in the system. The other connect goes to Relay 1 power pin (85).
The Pole (30) connection of relay 1 receives power from 20 amp fuse (12 volt aux condenser). Power will no flow through the relay and go out NO (86) connection via terminal strip (position 7) to the 12 volt Auxiliary Condenser Motor. At this time the air condition system should be working correctly. The thermostat will open and close as the temp criteria is met, the blowers will all be on.
The other mode is where the starcool is assisting the existing 12 volt air conditioning while the van is running. A 12 volt ignition on voltage is feed via the terminal block (position 2) to relay 3 Power (85). This will now remove power from the NC (87a) throw and provide it to the NO (87) connection which goes no where. In this case when we are running we remove power from of the specif components only needed when running 120 Volt shore power. One of those items is the 12 volt solenoid valve. So the freon system will revert back to assist mode.
A couple of key points, if not using shore power, make sure thermostat is not set to cool, and/or make sure the 120 starcool breaker is off. Make sure all the connections to the terminal strip are tight. If you turn off the van and the switches are still on you will hear various fans and such, but the air-conditioning is not working.
I know this response was late but may help others in the future.