Yet another A/C issue
Thread Starter
Instructor
Joined: Sep 2018
Posts: 165
Likes: 64
From: Lakeville MN
Yet another A/C issue
I have a 79 with a completely new factory air conditioning system. It was working perfect a few days ago but today for some reason when I turn on the a/c the compressor kicks on, blows cold air but the fan speed is stuck on low. The fan speed switch functions properly on any other setting (vent, heat, etc.) This one has me really confused. Any ideas out there? The fan blower motor resister and the fan control relay are both new.
Melting Slicks
Joined: May 2002
Posts: 2,716
Likes: 121
From: Sulphur LA
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
try the main control module, the main switch feeds the blower control then sends power to the blower resister.
the fan will run on low all the time, the low speed is fed straight form the AC fuse (on all the time), the fan switch will power the M1 & M2 speeds to the blower resister and High will be powered from the switch through the high speed blower relay.
did you change the control module in the center console?
Neal
the fan will run on low all the time, the low speed is fed straight form the AC fuse (on all the time), the fan switch will power the M1 & M2 speeds to the blower resister and High will be powered from the switch through the high speed blower relay.
did you change the control module in the center console?
Neal
Last edited by chevymans 77; May 9, 2020 at 07:30 PM.
Thread Starter
Instructor
Joined: Sep 2018
Posts: 165
Likes: 64
From: Lakeville MN
Yes, heater a/c control assembly is new. I've been researching this all afternoon with no really good ideas. Absolutely every single component of the air conditioning system is new except for the fan motor (which is not original, replaced by a previous owner)
Melting Slicks
Joined: May 2002
Posts: 2,716
Likes: 121
From: Sulphur LA
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
It can be frustrating but sometimes new parts fail, the switch needs to be removed and power checked at the back of the module/switch its self.
Neal
Neal
Thread Starter
Instructor
Joined: Sep 2018
Posts: 165
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From: Lakeville MN
I completely agree with you, new parts do fail (or don't function at all to begin with). Its very easy to find parts for these C3's but most are aftermarket. When I replaced the heat and a/c control assembly with a new one it didn't work properly, I only got air coming out of the vents. It was a bad vacuum switch, luckily I found a NOS Delco and it worked perfect. No substitute for genuine AC Delco when you can find it. I'll continue my trouble shooting.
Thread Starter
Instructor
Joined: Sep 2018
Posts: 165
Likes: 64
From: Lakeville MN
UPDATE: Just a loose connection at the fan speed selector switch. I unplugged it, cleaned the connections and put a spot of dielectric grease on each terminal. Works perfect, strange the the fan speed worked like it should in every mode except A/C but whatever, its fixed. BTW this was the first semi warm day up here in MN to really test the performance of the air conditioning system that I rebuilt in early spring, and I have to say I didn't have hi hopes, I wasn't expecting it to work as good as a modern vehicle but I was wrong. It works great, very cold! Its going to be a good summer!
Melting Slicks
Joined: Feb 2017
Posts: 3,235
Likes: 1,232
From: PHX AZ
Gralls..you sort of beat me to it....for a short while (sorry for the pun) I couldn't get High or medium....I unplugged the fan (purple wire in my car) cleaned the ends and Bingo.....worked.
Doesn't take much resistance to f the whole thing up!
Doesn't take much resistance to f the whole thing up!
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Thread Starter
Instructor
Joined: Sep 2018
Posts: 165
Likes: 64
From: Lakeville MN
Im so glad it was so simple. I was kind of heart broken after spending over $1000 on all new a/c parts and several days of work replacing everything and it only worked on low. Its fixed and life is good again.