AC not blowing when selected

[cbenge350]

I have a 73 c25 and then highest speed on my blower is not working, which i believe is the blower resistor. My question though is that when you select AC on the controls the blower completely quits on all speeds. Could both these problems be related to the resistor being bad? Didn't know if anyone has had this problem.

 

[Charlie]

Look at this thread

https://www.gmsquarebody.com/threads/ac-heat-high-speed-fan-not-working.27334/#post-520726

 

[chengny]

I have a 73 c25 and then highest speed on my blower is not working, which i believe is the blower resistor. My question though is that when you select AC on the controls the blower completely quits on all speeds. Could both these problems be related to the resistor being bad? Didn't know if anyone has had this problem.

Internet diagnostics are tough, but I'm going with a bad blower relay.

 

[gmachinz]

Check the ground @ the blower motor case-it may be loose or just rusty under the grounding ring.

 

[75gmck25]

If the '73 is like my '75, the high speed relay for the blower is controlled by the temp slider if its in Max A/C mode.

- When you move the temp slider over to Cold there is a detent about 1/4" before it reaches full max to the left. This temperature position will give you normal A/C and full control of blower speeds.
- If you slide it all the way over to the left (past the detent), you will be on Max A/C, which will put the vacuum doors in recirculate and the blower will stay on high speed.

My guess is that you have the temp slider all the way to left, so when you turn on A/C it is really be in the Max A/C mode and will only have the high blower speed. If the high speed relay is bad or the separate high speed fuse under the hood is blown, you won't have any air moving.

Bruce