AC/heat blower motor only blows low

[ryan_289]

Im starting the process into getting my Heater and AC working in my 78 C25 GMC. When I turn the blower on it only blows very lightly no matter where I put the switch. Can anyone tell me what I need to check to see whats going on? The guy I bought it from said the ac works but the line has a leak. Im about to find out because its starting to get hot outside!

 

[1987 GMC Jimmy]

Im starting the process into getting my Heater and AC working in my 78 C25 GMC. When I turn the blower on it only blows very lightly no matter where I put the switch. Can anyone tell me what I need to check to see whats going on? The guy I bought it from said the ac works but the line has a leak. Im about to find out because its starting to get hot outside!

Do you hear the fan speed up/slow down l, or is it just a single speed? Do you feel a lot of air deferring to the floor or maybe defrost? The line wouldn't have an affect on blower function, but you should go ahead an get that fixed so you don't spend a ton on freon. Your blower speeds, minus high, are controlled by the resistor, which bolts into the evaporator case and has prongs coming out of it. That's the first thing I'd check if you adjust the fan speed settings and it seems to run at the same speed. Pull it and see if it's burned. More information is needed, though, to better point you the right way.

 

[ryan_289]

No it feels the same no matter where the selector switch is. I ordered a new hose and drier on rock auto and found a mfg closeout on blower resistors for $3.99. I went ahead and added on to the order.

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[1987 GMC Jimmy]

No it feels the same no matter where the selector switch is. I ordered a new hose and drier on rock auto and found a mfg closeout on blower resistors for $3.99. I went ahead and added on to the order.

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That sounds like it maybe worth looking into further, but if the actual motor sounds the same at the different speeds, that's the best sign to me.

 

[ryan_289]

Well I got home and dug a little further. Apparently when I was feeling air was when I was driving down the road. Sitting still in my driveway I get nothing. I took a look at my fuse panel and the ac fuse is out and the top spring holder for the fuse is gone?

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[ryan_289]

I have power to the resistor on the blower box when the key is on at all 4 terminals but no fan. I'm guessing this extra fuse maybe is the wire around from the fuse block?

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[ryan_289]

Only the green compressor wire is plugged in here. Is there supposed to be another wire plugged in next to it?

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[ryan_289]

I think I've got it narrowed down to the blower motor. I get power at the purple wire at the blower and at full blast on the switch I can hear the relay click. I removed the blower and put 12v to the spade terminal and ran ground to the housing but got nothing. Using a test light shows the housing to be hot.

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[Rusty Nail]

Good job.

Pull it out and hook it to the battery terminals!

 

[ryan_289]

Yep bad blower motor. Put a new one in today and it blows air again. The only issue now is that whenever you turn the key on, the fan blows on low all the time. Even with the ac selector off. When it's off it will not change speeds but will change speeds when the ac selector is slid over to the right?

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[smoothandlow84]

That sounds about normal. The fan will circulate fresh air all the time into the cab. When you slide the control lever to the passenger side...max, normal, bi-level defrost. ..etc. The system uses vaccum pressure and opens and closes the required vents needed to facilitate the selection. The next step is to install a shut off valve in line on the heater hose coming OUT of the motor. By installing a shut off valve, not only will this prevent unwanted HOT air to circulate through the cab in the dead of summer, but it will also stop coolant from entering the cab if the heater core decides to leak under the dash.

 

[chengny]

Yep bad blower motor. Put a new one in today and it blows air again. The only issue now is that whenever you turn the key on, the fan blows on low all the time. Even with the ac selector off. When it's off it will not change speeds but will change speeds when the ac selector is slid over to the right?

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As Steve explains, the airflow into the cab from the blower can never be completely turned off. The blower will operate at the low speed setting even with the mode select lever in the OFF position. When MAX AC is selected the blower will only operate on the highest speed.

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These systems are of the reheat type. Some flow of hot engine coolant should be allowed to the heater core - this is explained below:

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