Quote:
Originally Posted by FAKKY
Drier Pressure switch => Pin 86 on relay (other wire on switch goes to Evap Unit in car). Grounded. 12v+ from ign on other wire.
Ground -> Pin 85 on relay
+12v feed to both AC compressor and condensor fan -> Pin 85
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I think you mean pin 87 on that last one.
also, think of an automotive style relay as a low current to high current switch. pins 85 and 86 are the low current switch, and pins 87 and 30 are the high current switch. energizing the low current contacts engages the high current ones. so if you only have a low current 12v (-) trigger available and need a high current 12v (+), using a relay set up with your 12v (-) trigger on 85, you would use 12v (+) on 86 (to energize the relay and connect 87 to 30), a high current 12v (+) feed on 87, and the output devices on 30. some people wire a relay backwards, with input on 30 and output on 87, but that is not the way the relay should work, more on that in a second.
so when you say you are using the low pressure switch as one side of the relay, I am a little confused when you talk about grounding the same pin. a low pressure switch is a switch, with two wires, its a normally open switch so that means that the two contacts are open unless there is suitable pressure, and then it is closed, and whatever you have on wire one is what is on wire two. I would set it up grounded because its easier aand safer than as 12v. just ground one wire on the switch, doesnt matter which. the other wire will have ground as long as there is pressure in the line.
so if you wanted to make it work with a low pressure switch (-) interrupt and a 12v (+) switch in the cab, you would wire as
85 (-) from low pressure switch
86 12v (+) from switch on dash
87 FUSED high current 12v (+) (10 ga or better! fused at the battery!)
30 wired to fan and ac clutch.
I would probably use two separate relays for the fan and for the ac clutch because mixing high current (fan) with low current (clutch) can burn up the low current wire with a short, the high current wire fuse wouldnt blow till the smaller one was on fire.
this way, if the low pressure switch opens (low pressure) with the ac turned on in the cab, it wont turn the relay on.
if you have fan triggers in your pcm, you can wire a SECOND relay to that first using
85 (-) pcm trigger
86 12v (+)
87 FUSED high current 12v (+)
30 to 87a on the first relay.
this way, the pcm can turn the fans on for any cooling reason, and when the ac is turned on it holds the fan on if the pcm shuts off.
using 87 as input is the reason this works, the pcm will turn on the fan relay and it will flow from 87a to 30 on the AC relay without energizing the relay. obviously, in this case you will need that second ac relay I talked about so that the pcm doesnt kick on the AC clutch when it turns the cooling fans on.
I can draw all this out, sorry it was long, but i think understanding how it works is better than just pumping out a diagram.