47-55.1 wiring a/c condenser fan

[evilokc]

I want the fan on my a/c condenser to come on when I turn the a/c on. cant I wire the fan power to the power wire on the "on" switch of the a/c controls? seems right.

[evilokc]

I ran it through a relay and its still not working. the knob to turn the a/c on is a rotary knob. will that make a difference?

[joedoh]

Originally Posted by evilokc

I want the fan on my a/c condenser to come on when I turn the a/c on. cant I wire the fan power to the power wire on the "on" switch of the a/c controls? seems right.

you cant wire a high current fan to a low current switch. sometimes there is a transistor in the controls but other times its just an extra set of contacts and either of those are only capable of at most 0.5A or less of current, which is fine for triggering a relay or the compressor clutch (which itself is a relay), but will not come anywhere near supplying the 20-30A required by an electric fan.

make certain you have the relay wired correctly,

for a quick primer on a standard automotive relay, pins 85 and 86 are the low current switch and to close that switch you need 12v+ on one side and 12v- on the other. it doesnt matter which is which, if you have a 12v+ output from your controls then you wire it to one of those pins and the opposite, in this case a 12v- (ground) to the other. if you have a grounded output, you wire it to pin 85 or 86, doesnt matter which, and on the other side a simple 12v+.

pins 87 and 30 are the high current switch, you put whatever you want to come out of pin 30 on pin 87, in your case you want a 30A capable 12v+ output from pin 30 so you wire a heavy gauge 12V+ to pin 87 and when the low current switch (85 and 86) is energized, pin 87 connects to pin 30 and you have your high current output.

now for the bad news. if your controls have a transistor or a simple contact to energize the compressor clutch (usually what that wire is for) and you wired it to a fan without a relay, you may have burned up the transistor or the contacts. current draw is kind of like a greedy ex, it doesnt really care what you are capable of giving it wants everything you have, until you are dead. so if you hooked a 30A fan to a 0.5A set of contacts, chances are good that the little contacts tried vailiantly to pay the bigger bill before expiring. put a VOM on the wire with nothing else hooked up and see if there is indeed a 12v+ output still available when you turn the control on. if there is, re-read the relay portion above. dont forget a fuse on your high current supply wire, no more than 6 inches from the battery!

[_Ogre]

a rotary fan switch would be low voltage at low fan speed and probably wouldn't activate the relay
your typical aftermarket ac unit should come with a trinary switch, google trinary switch wiring diagram

[joedoh]

Originally Posted by _Ogre

a rotary fan switch would be low voltage at low fan speed and probably wouldn't activate the relay
your typical aftermarket ac unit should come with a trinary switch, google trinary switch wiring diagram

did you read it differently than me? I didnt think he was hooking it to the blower output, but to the ac on switch that is usually an output for turning on the compressor.


evilokc maybe explain which output you are talking about