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Old 05-24-2010, 09:27 PM
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fan shuts off on high

well iv been through alot of trouble getting my a/c to work and today i finally got it all finished up and charged, new compressor, dryer, orifice tube, cleaned the system out, its all good to go. the problem is if i run the fan on high it seems like it only will run like that for about 5-10 minutes and then the fan shuts off. it wont work again untill i give it a break for a while. i used to be able to keep the fan just short of full and it would be fine as long as i didnt put it to full, but on my way home today it shut off and it was 1 click short of full, so something is on its way out but i dont know what? could it be the blower motor resistor or blower motor itself or is the actual controll unit in the dash?

the truck is a 95 chevy half ton.

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Old 05-25-2010, 07:41 AM
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Hi let's move this to General Rodding Tech.

Dan
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Old 05-25-2010, 08:49 AM
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Hi let's move this to General Rodding Tech.

Dan
sorry, wasnt sure where to put this one.
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Old 05-25-2010, 09:32 AM
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On the older trucks the lower speeds run through the resistor pack, but the high speed uses a separate relay and a separate fuse. When that fuse blows you lose high speed.

It sounds like your fan is drawing too much power on high and you might have a self-resetting breaker that powers the high speed. If you can verify the amperage draw, that would be the best way to verify blower power draw problems. However, replacing the blower motor in most trucks is fairly easy and not that expensive, so it might be worth it to try a new one.

Bruce
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Old 05-25-2010, 09:42 AM
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the way you describe it, it becomes clear that the problem is not in the control unit on the dash but rather in the blower motor itself. your right, it is cheep and easy to replace the blower motor, probably worth doing anyway since my fan doesnt seem like it blows as much air as it used to.

thanks for the reply.
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Old 05-25-2010, 03:19 PM
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replaced the blower motor and resistor. one of the coils on the resistor looked blue like it had gotten hot, after seeing that i was pretty confident i got the fix. so i cranked the fan up to full and it worked great, left it running while i went to put my tools away and by the time i got back the fan was shut off like it usually does after running it on full for a while. what could it be now?
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Old 05-25-2010, 03:46 PM
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Quote:
Originally Posted by chevy1500z71
replaced the blower motor and resistor. one of the coils on the resistor looked blue like it had gotten hot, after seeing that i was pretty confident i got the fix. so i cranked the fan up to full and it worked great, left it running while i went to put my tools away and by the time i got back the fan was shut off like it usually does after running it on full for a while. what could it be now?
Check the connector on the control and all the wiring. They are known to overheat and ruin both the harness end and the switch.
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Old 05-26-2010, 10:08 AM
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Originally Posted by T-bucket23
Check the connector on the control and all the wiring. They are known to overheat and ruin both the harness end and the switch.
well i took the dash apart and inspected everything and the harness looks fine, i can change the switch without replacing the whole control unit so ill do that and see if it fixes my problem. ill report back when it doesn't work lol.
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Old 05-26-2010, 12:10 PM
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Instead of buying more parts, why not troubleshot with a meter to see when it dies where the voltage is going away. You have already bought parts you didnt need
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Old 05-26-2010, 12:42 PM
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Quote:
Originally Posted by chevy1500z71
replaced the blower motor and resistor. one of the coils on the resistor looked blue like it had gotten hot, after seeing that i was pretty confident i got the fix. so i cranked the fan up to full and it worked great, left it running while i went to put my tools away and by the time i got back the fan was shut off like it usually does after running it on full for a while. what could it be now?
You may have a bad blower control relay. In any event, it's easy to check:

When on high, the relay's #4 terminal is energized- this causes the upper contacts to open and the lower contacts to close, which in turn allows current to flow through the #3 terminal of the relay, through the line fuse, and then on to the blower motor.
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Old 05-26-2010, 01:46 PM
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well the fan switch was a waist of money, still the same problem. im glad i bought the fan tho, my original fan was very week.

is the blower controll relay the one behind the glove box infront of the resistor? if so, that is where im hearing a clicking noise come from right after the fan shuts off...
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Old 05-26-2010, 02:11 PM
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Quote:
Originally Posted by chevy1500z71
is the blower controll relay the one behind the glove box infront of the resistor? if so, that is where im hearing a clicking noise come from right after the fan shuts off...
That is correct.
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Old 05-26-2010, 02:16 PM
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It can be checked w/a test light or meter, before replacing it.

If the motor itself has a thermal overload protection switch, it might be tripping (is the motor HOT when it stops running?) because of a clogged or non-functioning air plenum or a blocked vent/air intake that would cause the motor to labor against a "vacuum", so to speak.

If the motor is cool, or not HOT, then I'd suspect the relay.
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Old 05-26-2010, 03:48 PM
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Quote:
Originally Posted by cobalt327
It can be checked w/a test light or meter, before replacing it.

If the motor itself has a thermal overload protection switch, it might be tripping (is the motor HOT when it stops running?) because of a clogged or non-functioning air plenum or a blocked vent/air intake that would cause the motor to labor against a "vacuum", so to speak.

If the motor is cool, or not HOT, then I'd suspect the relay.
well i replaced the relay just becasue they gave me store credit on returning the fan switch so i figured why not. no help.

the fan motor gets a little warm(barely), not hot. but, when i replaced the fan i noticed there is a large filter in front of it, it felt dirty and im sure its totally clogged now that i think of it, the passenger side gets very little air out of the vents compared to the driver side, it got alot better with the new fan but the problem is still there. how do i get to this filter to change it/clean it?
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Old 05-26-2010, 03:59 PM
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Quote:
Originally Posted by chevy1500z71
well i replaced the relay just becasue they gave me store credit on returning the fan switch so i figured why not. no help.

the fan motor gets a little warm(barely), not hot. but, when i replaced the fan i noticed there is a large filter in front of it, it felt dirty and im sure its totally clogged now that i think of it, the passenger side gets very little air out of the vents compared to the driver side, it got alot better with the new fan but the problem is still there. how do i get to this filter to change it/clean it?
What year is this truck. Is it a single wire on the fan motor. It would be interesting to use a meter or test light on the connector at the fan to see if when the fan stops the power goes away. You need to logically eliminate parts one at a time until you get to the root cause of the problem. If you still have the old fan, plug it in and let it sit on the floor or hang and see if it shuts off. If it is an older truck, most didnt have filters. You may bee looking at one of the blend doors.
Once you use a meter or test light you will get to the root of the problem quickly.
The other thing to look at is you may be loosing the ground, its not likely as you say it still works on lower speeds when high doesnt work. If this is true it eliminates the fan thermal protection being the issue.
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