heater help please

[GENERAL76]

Hi, I have a 76 silverado with AC, my heater worked great until the blower switch began sticking and finally locked up. now the blower motor doesnt work at all , not even the constant low. So I bought a new switch, and nothing. I went ahead and bought all new parts, resister and relay and still nothing. Whats confusing me is that Im getting 14 volts to the relay and no power to the motor, the motor works fine when I jump it to the battery or jump it from the orange power wire that goes to the relay. I havent ever seen test figures for these components to check if they are bad or not, so I compared the figures from the old and the new (I just checked them for resistance and continuity) and they are real close, no open circuits and very low resistance. Can someone tell me where I might be losing power from the relay to the motor? any help would be appreciated,  Thanks.

[ccz145a]

check the relay

[VileZambonie]

Did you check the fuse? Theres one inline in the engine compartment and one in the fuse box. If ok check all of your connections

[GENERAL76]

The relay is new, how would I check it without any without any numbers to go by? I just figure that if there is not any open circuits or extremely high resistance its ok, but how would I know if it is supposed to have high resistance without any references, the Chiltons and Haynes are way to vague and generic in these kind if areas. I looked at both fuses, they both are not burned or melted, Ive owned the truck for eight years and never had to change a fuse, but Im not the most familiar with the glass fuses, can they be bad without looking like the obvious bad fuse? Would I still be getting full voltage to the relay if the junction block fuse was bad?What does that fuse protect that the interior fuse doesnt? Hey Vile, I printed off one of the hvac schematics  you had in another post and it is the only one that Ive ever seen that is accurate down to the color, is that out of shop manual? Any way you guys are great and I thank you for your help   Thanks

[78 Chevyrado]

If all else fails, look inside the new relay.  Pop the cover off and see if there's a resistor inside there across two of the terminals.

 My Original GM  relay didn't have a resistor, but the new one I bought did and it kept popping fuses and burning up the relays.  Finally I swapped the new one I'd burnt up one in for a new relay and simply snipped off the resistor before I installed it and now it works fine. 

[VileZambonie]

General is this the thread you are referring to?

http://forum.73-87chevytrucks.com/smforum/index.php?topic=12793.0

[GENERAL76]

Thats a good idea Ill give it a try, I did notice the resistance was a little higher in the new one than the old, but but only one or two ohms so it never crossed my mind, Ill probly change the fuses out anyway because who knows how old they are, couldnt hurt. Yes thats the diagram I printed off, I must have studied it for three hours last night trying to figure out just how the current travels, like is the power from the junction block to the relay powering the switch to the resister, and is the relay the first or last in line in the system?

[VileZambonie]

It's fairly simple. Everything is in the schematic. The 30A fuse in the engine campartment goes to the blower relay. The 25A fuse in the cab (ign fuse 3) goes to the selector switch. There's your two B+ you have the ground ckt and all of those connections that usually cause opens in the circuit. Check and clean them carefully. Wiggle test your connections. If you find an intermittent just rewire it. I rewired the whole system on my 74 and located all of the circuitry to the inside of cab under the dash to hide it.

[GENERAL76]

That makes sense, I opened both relays and there was no resister in either one so I tried to figure out how the relay operated-power from the switch circuit energizes the coil turning it into a magnet which pulls the plate down connecting the points and allowing the power from the junction block to go to the motor. I hooked up both relays and manually pushed the points together and it worked so I figured the relay is not the problem and can only do its job if it has power to the coil, well I tried to see if it had a bad ground( 150) by grounding it on the negative post on the battery nothing, so I used the original ground and hooked a wire to the positive side(52) and jumped it to the battery, bingo! It magnetized and the points came together and it worked, so I think the problem is in switch department, the new switch I bought didnt have the extra 52 tang( I guess thats what its called) so I soldered a short wire to it to connect that single orange wire, now if I stick the voltmeter to the 50B on the switch harness will I get 12 volts to it? Looks like I need to be looking around the switch, control panel, and fuse box for the problem, any ideas?

[GENERAL76]

Well, Im not getting power to the selecter switch 50A/51 terminal, Im getting voltage from the fuse box connection 50 when I disconnect the wire from it, but when I leave it connected I dont get voltage from the 50A/51 terminal in the selecter switch harness, I tested the 50A brown wire for resistance and got none and it has continuity from both ends and the terminals are shiny and clean. Im going to replace the fuse and possibly remove that wire(50A) and put a new wire in it, does anybody know if Oreillys or Autozone carry the terminal ends that go in the plastic harness or will I just have to make my own?

[VileZambonie]

Let's put the schematic in here to make it easier

[VileZambonie]

Did you check both sides of the fuse for B+?

[GENERAL76]

Well, it was the fuse, I feel like an idiot! The old fuse must have been really old, it just wore smooth out, it wasnt burned or broken it just looked like the inside was oxidized and corroding from age. Its always the easiest things that get me, but if I would have replaced it from the start I wouldnt have fully understanded the system like I do now so it was worth it. Im going to get the AC delete cover eventually, and Im torn between pulling the wiring inside like you did or going with the control panel and harness from a non ac truck. Im probably going to go the inside route but if I got ahold of the stuff from another truck, what would be some hurdles I might run into? Also where did you put your vacuum ball and did you just make your purple motor wire longer? Thanks for all the help you guys have given me I appreciate it.

[VileZambonie]

If you move the wiring and resistor to the inside just be careful. You need to make sure the resistor doesn't touch the heater core and that it gets air circulation or you can burn the house down. I hid all the wires and such but left the vacuum cannister. I just charged up my camera and I'm cleaning my garage today so I will try and take some pics for you.

[GENERAL76]

Pics would be nice, the last time I looked down there there didnt seem to be a lot of room for that stuff. Thanks