Been having trouble finding the problem on a '91 S10 pickup. Has a/c. Not getting high speed on the heater fan motor. Motor works fine, resister coils all seem to get hot on various settings. If I start the truck all I have is low. If I get out and give the relay a flick with my fingernail, the fan starts into high. Tried two used relays and a brand new one, all do the exact same thing... even with the relay unscrewed and sitting in the palm of my hand (isolating the impact from everything else). Checked the resistor. Checked the contacts. Clean and tight. The problem is intermittent, usually happens on start up, about 50% of the time after I do flick it once it is fine to switch speeds for the remainder of the trip, the other 50% if I change speeds it goes back to low only. I'm at a bit of a loss on this one. :Banghead
Check voltage and ground to coil of relay, could be a low voltage condition, back probe the + pin of relay with relay energized to check for voltage drop.Just a tought but your tap could be enough to throw the contacts in the relay all the way together, with low voltage.. Good Luck
I was thinking along the same lines, but I don't know which pin does what on it. There are 5 if I'm not mistaken.
Derek, unplug the relay find the one that has voltage when the fan switch is in the high position, you should have 4 wires to the relay one is hot at all times this is supply voltage to your load, one that is the load (blower motor), one ground for relay coil, and one hot when in high position to energize relay. There may be five wires in some applications, but thats not important here. Find the one that powers up with the high position, then find the ground on plug using a voltmeter, if the voltage is low ( below battery voltage ) you have a bad connection or wire somewhere. If you have battery voltage plug the relay back in, and use your voltmeter leads to test from the backside of connector to both wires, with the switch in high position. Voltage should remain close to batt voltage. The wires your looking for will be the small gauge wires on the connector also check the terminals very close at the relay connector, I've seen alot of problems on all kinds of equipment in relay connectors.