Blower motor

[Happytexan]

Hello all. This is my first post on the forum. Truck data first: 1974 C10 Cheyenne super, factory 454, factory a/c still working (with an issue), th400, 2wd, factory 3:73 12 bolt out back.

the a/c blows ice cold but only blows on high. That was the only issue with the a/c until I remounted the recirc door actuator someone had left dangling so they could install kick panels with speakers now the recirc door operates as it should, but it still only blows on high and it stops blowing after 10~20 minutes, then will start blowing again if I turn the a/c off and back on. Sounds like a circuit breaker to me, but I can’t find one. I have replaced the resistor, blower relay, and blower motor. Not firing the parts cannon, just freshening things up while I’m in there. Side note, key on engine off, the blower blows on low speed like it should. As soon as I slide the mode switch from off to a/c it stops blowing, if it’s acting up. Is there a circuit breaker for the blower motor I’m not seeing? Do I need to pull the hvac control panel and dive into that? I greatly appreciate your time and help.

[bd]

No circuit breakers from the factory.  Verify that the blower motor case is suitably grounded by a dedicated ground wire firmly attached to the motor flange.  Check the purple wire for a clean and firm connection to the blower motor.  Check the inline fuse that connects to the firewall junction block (15-amp spec'd, but 20-amp is common) - the plastic holders have a propensity for melting because of connection issues that generate excessive heat exacerbated by engine compartment heat.  If the holder is melted, convert it to an Mini-ANL 20-amp fuse and holder.  Note that the inline fuse is only for supplying high blower speed via the blower relay, so make sure the relay connections are not compromised - inspect connectors for melting.  Intermediate blower speeds are powered through the blower switch.  Use a test light to probe for power at the resistor in low and medium switch positions.  The blower switch receives power from the mode selector switch - if the resistor is dead then remove the dash control head and check the selector switch and blower switch connections and functions.  The selector switch is plastic and subject to connection issues and resultant overheating that burns the switch.  As you follow power from one switch to the next, replace switches and connectors as needed.

[Happytexan]

Thank you! I used a rollock disc to take the paint off the mounting hole that the blower ground wire is on. It may take me a few days to check everything and post back with family visiting for Independence Day. Stay safe and have a good weekend.