Uhrlto

I hope someone can help in this matter. I had low air output from my AC vents so I thought it was the blower motor. Its original so its 28 years old. I replaced it with a new one

and the air out put is the same. What gives? Is there something that I missed when I replaced it? I checked the area for any foreign matter and found nothing along the path that the motor
blows through. As Summer is around the corner I could use some advice. As always many thanks.

1986 c4

Tony

billschroeder5842

Blower motor resistor.

auto_cran

Tony -

I had the same issue when I acquired my 84 Corvette. The paper work that came with the car said a shop had installed a new blower motor - but still, the output out of the vents was next to nothing, even on the highest setting.

Lots of digging around, and I discovered my issue - it may/may not shed some light on yours, but here is what I found. Warning - I fixed mine about 2 years ago, so going off of memory here....

At the back of the motor (of the car -not the blower motor!), near the distributor - there is a very thin vacuum line that comes off the engine, goes into a little checkvalve device, then goes off to the passenger side of the engine, eventually going into the main wiring harness and entering through the firewall in to the cabin. In the cabin, you can find the other end on the passenger side near the transmission hump. For the HVAC to work correctly, it needs engine vacuum.

On mine, this line had been compromised (it had been melted) on the passenger side of the engine compartment, over near the pipes used for the heater and ac (before entering the main wiring harness). Once I fixed the line, the air out of the vents was greatly improved.

The line in question is a very thin vacuum line. It looks to be made out of plastic, not rubber and is shiny black. You'll know it when you see it.

Again, not sure if this is what's going on in your car, but for me it resolved a very frustrating issue.

Good luck - and let us know what you discover.

Chris

Cruisinfanatic

I'll have to look for that

Hot Rod Roy

As the vid in -post #2 says, that's for the '90-'96. Totally different than your '86. I don't know why some people think all C4's are the same.

If your only problem is the fan speed, the vacuum line is not the issue. The vacuum line selects the a/c, vent, heat, or defrost functions. Can you select those functions?

Can you hear the fan changing speed when you change the speed selector switch? The fan speed is a function of the fan speed switch, the resistor network, the fan relay, and the fan motor.
Do you have the FSM for your car? Do you have a DVM (Digital Volt Meter)?

Uhrlto

Thanks Chris for your reply, I do tend to agree with Hot Rod Roy about the vacuum situation. However for grins and giggles I did check that line as I remember that I had to fix it when I first bought the car. It was broken where it came through the firewall and I replaced it with new vac hose all the way to the programmer module. Its still ok.
Thank you again

Tony

Uhrlto

Thanks Bill.
Of Course it has to be that part, It expensive...Going to try a couple of things first before I lay out 165.00 bucks. If I'm reading the FSM right if I short out the plugs i.e. full 12volts to the upper right pin of the second 3 wire plug as shown in this video that should make the blower come on full power, at least that is what I hope.

Thanks again

Tony

Uhrlto

Thanks Roy,
To answer you questions, yes, all the functions work on the c68 control head. They did not when I first bought the car as i had a ton of problems with the programmer and the control head. I rebuilt both with parts from Batee.com and fixed the black vacuum lead coming into the car. I replaced the fan blower just a few days ago as the old one is 28 years old and I figured thats what was causing the low output. Wrong. Yes I can hear the fan slowing down from 10 on the head unit to almost no air at all at 1. I have a FSM for my 86 and am looking at the fan relay as well as trying to short power from the 12volt supply to the second connector as shown in the video to sim full power on the blower. The resistor, as you probably know is expensive and if I need one going to try an cross match to a different car to find the same but less expensive if possible. Oh, yeah I have a meter as well.

Tony

Hot Rod Roy

Tony, I broke one of my own rules: If I'm not sure about what I'm about to post, don't post it.

I wasn't aware you could get the C68 electronic a/c controller in the '86. Please ignore my comments. Sorry.

Tony, I just checked your math from your post #1. 2020 minus 28 years is 1992. What gives?

Uhrlto

I flunked math in High School. hahahahahaha

Ok, so I have a 34 year old car,thank God for caulculators...and micro soft for spell checker

So I went and shorted out the 12 volt lead on the 3pin plug to the 4 pin plug fan motor lead which should have given me full power to the motor and full air out the vents and its still the same. This is beginning to make me wonder if the hot cold door is open all the way for cool or I have a blockage at the evaperator. would you agree with my logic Roy?
And dont worry about the C68 AC, from what I understand the PO ordered it when he bought the car new in 86. They normally came with a manual AC (which I would much prefer.
Tony