Heater & A/C blower doesn't work on high speed

[batcomm1]

I'm having an issue with no high speed but all other speeds work fine, is there a location for a high speed fuse only to check?

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[bd]

What year/model truck?  Does it have an inline fuse connected to the firewall junction block stud?

[batcomm1]

84 Silverado

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[batcomm1]

84 Silverado

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Has all speeds but high, ran a 12v directly to it, got nothing, but as I said still works on all speeds but high...

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[batcomm1]

Here ya go

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[bd]

Has all speeds but high, ran 12v directly to it, got nothing, but as I said still works on all speeds but high...

You ran 12v directly to what?  The blower motor?

[batcomm1]

Has all speeds but high, ran 12v directly to it, got nothing, but as I said still works on all speeds but high...

You ran 12v directly to what?  The blower motor?

Correct, was a test with the switch on ....was advised to try it and was told the blower would come on high if it was good

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[bd]

If the blower motor runs at low and medium speeds, the motor works.  Does the blower relay "click" when you select high blower?  Do you have a test light?

[batcomm1]

Do have test lights and meters. I'll have to check for the relay "click"

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[bd]

Use an incandescent test light and probe for I+ on the orange wire (Ckt 52 in the diagram, below) at the blower relay with the blower switch set to high, mode switch set to AC, and ignition switched ON.

[batcomm1]

Have light/12v on the orange in those listed conditions

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[bd]

Did the relay "click?"

• Yes - With the blower on "High," probe the red (Ckt 2, B+) and purple (Ckt 65, blower motor) wires at the blower relay.  Do both illuminate the test light equally bright?
• Yes - The blower motor should be running.
• No - If both wires are dead, repair the open in the red wire between the relay and firewall junction block, or restore B+ power to the junction block, as needed.  If only the purple wire is dead, replace the relay and review the topic, "Blower Motor Relay info (Keeps blowing fuses)".


• No - Clip the test light to the battery positive post and probe the black wire (Ckt 150, ground) at the blower relay.  Does the test light illuminate?
• Yes - Replace the relay and review the topic, "Blower Motor Relay info (Keeps blowing fuses)".
• No - Repair the open in the relay black ground wire or the ground wire's connection to the cab sheet metal, then recheck the high blower function.

[batcomm1]

Might be a dumb question but...am I testing these with the relay plugged in or just on the plug end off the relay

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[bd]

Wires must be connected to the relay but the relay can be unbolted from the evaporator housing if that makes for easier access.

[batcomm1]

So...I've only got power on the right side (battery side) of this...I'm assuming it has an internal fuse? If I jumper it across all works perfectly!!!

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