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1994 Chevy Astro heat and air selector only works on fourth

Tiny
CARLSATURN
  • MEMBER
  • 1994 CHEVROLET ASTRO
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 250,000 MILES
I can only get my air and heat selecter to blow on the fourth position only. On high or low it will not blow at all. Iv replaced the blower, the switch, and a relay located above the blower and still get the same result. Fuses are all good. Where to from here?
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Monday, March 30th, 2009 AT 2:54 PM

14 Replies

Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
Usually turns out to be the resistor, but can be the switch, test it this way:
BLOWER MOTOR OPERATES AT HIGH SPEED ONLY 1. Turn ignition on. Set blower switch to speed that does not operate. Connect test light between wire of inoperative speed position at blower switch and ground. Low speed is Yellow wire; medium speed is Light Blue wire. 2. If test light does not glow, replace blower switch. If test light glows, connect test light between Yellow wire or Light Blue wire (depending on switch position) at blower resistor and ground. 3. If test light does not glow, repair open Yellow wire or Light Blue wire between blower resistor and blower switch. Go to next step if test light glows. 4. Connect test light between Orange wire at blower resistor and ground. If test light glows, circuit is okay. If test light does not glow, replace blower resistor. Page 1 of 1 HEATER SYSTEM -1994 Chevrolet Astro 3/30/2009 There are two relays, one in the cab fuse block the other for high blower on the relay brackett on right rear of engine compartment. The reisitor is on the blower case.
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Monday, March 30th, 2009 AT 2:59 PM
Tiny
CARLSATURN
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  • 8 POSTS
Like I stated in my question the switch is new. Ive heard about this resistor but I dont know where it is or what it looks like. Can you help me with that? Any chance of a picture? My blower only operates at the position just before the high position. Nothing above nothing below.
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Monday, March 30th, 2009 AT 5:14 PM
Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
The risitor is on the plenum, the fan motor plug plugs into it and so does the switch harness. Usually it's pretty darn close to the fan motor!
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Wednesday, April 1st, 2009 AT 2:43 AM
Tiny
CARLSATURN
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  • 8 POSTS
Have no clue where this resistor thing is. Have no clue what a plenum is either. I know your trying to help but I dont understand. If not a picture maybe a drawing or something? Any book I can buy that will show me what the heck iamm looking for?
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Wednesday, April 1st, 2009 AT 7:06 PM
Tiny
MERLIN2021
  • MECHANIC
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On the right side look up under the dash, the plenum is the big black air box for the heat, the blower and resistor is on it. Sorry I cant find a picture. We do the best we can.
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Thursday, April 2nd, 2009 AT 1:24 PM
Tiny
CARLSATURN
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  • 8 POSTS
Thanks for your help. I do greatly appreciate it. I;ll keep looking. Iam glad for your site.
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Thursday, April 2nd, 2009 AT 5:27 PM
Tiny
CARLSATURN
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  • 8 POSTS
I finally found the dreaded resistor. Replaced it and still have the same problem. Switch only works on the fourth position. The position just before the high position. So now ive replaced 1the blower2the switch3the relay on the engine side4the resistor. Is there any thing else that I can check? Iam at a loss!
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Sunday, April 5th, 2009 AT 2:23 PM
Tiny
MERLIN2021
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Did you do the testing I posted? If not since you now have found the resistor, and switch, perform the tests! It now appears to be a bad wire, maybe the orange one. Also check the grounding of the blower motor.
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Sunday, April 5th, 2009 AT 2:54 PM
Tiny
CARLSATURN
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  • 8 POSTS
I just printed out the test you recomended. I;ll do those nent. A question I have is you say at the end there are two relays on in the cab fuse block and the one on right rear of engine compartment. By cab fuse block do you mean wher all the other fuses are under the dash? Is it one of those sliver looking ones there are two of those I see and on the right rear engine do you mean the side of the blower as when iam facing, looking at the engine?
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Sunday, April 5th, 2009 AT 4:24 PM
Tiny
MERLIN2021
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The silver ones are for the blinkers and four way flashers. I will try to find oictures for you, but if you have the owners manual, it should have a diagram of ALL fuses and relays.
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Monday, April 6th, 2009 AT 2:47 AM
Tiny
CARLSATURN
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I did the test you said do and every thing checked out ok. Each and every position showed a light on my tester so iam really at a loss here. Ive checked rechecked everything I can think of!It still only works on forth.
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Sunday, April 12th, 2009 AT 10:54 AM
Tiny
MERLIN2021
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It tested OK at all sections means the wires and resistor are OK replace fan motor, or check the ground for the fan motor.
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Monday, April 13th, 2009 AT 2:50 AM
Tiny
CARLSATURN
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  • 8 POSTS
I have replaced the fan motor. That was the first thing I replaced. The fan runs on the fourth position only. How do I check the ground on it?
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Monday, April 13th, 2009 AT 5:19 PM
Tiny
MERLIN2021
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It's on the right side of the radiator, on the support, near the headlight. did you test the relay as outlined?
Here's the wiring diagram if the purple wire has power in all positions, but the fan only works in hi, then either the relay, ground, or blower is defective, run a fused jumper from Battery to the blower motor and one to ground, does it work?


https://www.2carpros.com/forum/automotive_pictures/62217_Graphic_18.jpg

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Tuesday, April 14th, 2009 AT 1:01 PM

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