Over the past few months the number 4 switch was blowing high, then it would blow very faint and then hard again, now its out completely and only 1-3 work.

We replaced the resistor, no luck and I just got done replacing the AC switch for number 4 and number 4 still doesn't work.

Am I missing something?

Only thing I haven't replaced is the motor itself.

 

Any idea?

 

Try improving the ground to the relay under the hood. It is mounted near the middle of the firewall. I took a heavy gauge wire about 10" long and put a ring terminal on one end and a blue 'crimp-on' splice on the other end. This will be the new, improved ground wire.
To install it: Use a 10 mm socket to remove the Relay hold down bolt from the firewall. Now you remove the connector from the resistor. I believe there are five wires eminating from that connector. You want to splice the new ground wire to the black wire going to the connector. I believe it is the second wire from the top of the connector as installed. Crimp the new ground wire to that black wire. You see why you pulled the relay off and disconnected the connecotr from the relay!? (It makes it easier to crimp the splice on that small black wire.) You now need a convenient place to bolt down the other end of the new ground wire with the 'ring terminal'. Put it on the same 10 mm bolt that holds the relay to the firewall. Then install the relay and snug down the 10 mm bolt and you are done.
Please note: I did this additional ground wire on my '03 Blazer because the 1-4 switch on the dash was getting too warm. I think you may have burned out that new relay you just installed because of the poor ground? IOW now you have a good ground , you may need to purchase another relay. Try this and let us know how it turns out.

 

change the blower motor under the passenger side the fins are starting to go .it's easy couple of blots unplug and put the new one in. cheap part at any auto parts store

 

Jason, when you siad you replaced the 'resistor' I assumed you were referring to the 'relay' on the firewall. Did you mean the resistor on the blower housing? Also is the switch **** for the 1-4 fan getting warm when the fan is on?

 

We replaced the blower motor fan speed resistor and then I replaced the number 4 switch. The switch doesn't get hot when on number 4.

Also sometimes when on number 3 the speed will act like it's on number 1 or 2 and then after several seconds it will back back to the level 3 speed.

 

Some good info on 1997 Blazer with fan speed problem.
https://blazerforum.com/forum/2nd-ge...rk-high-86003/

 

Which of these photos show the high blower relay?

 

I have a 2003 two door and I see you have a 1999. None of the three photo's show what my relay looks like. It is a little higher on the firewall and slightly to the left of the center. Apparently the location changed. I wish I had the ability to post a photo, but I don't.

While re reading your posts , I am struck by the intermittent nature of your symptoms. My SUV's symptoms were always consistent, so maybe my experiences won't be helpful to your case. However, I should mention that a bad ground can cause intermittent problems.