austinado16
Full Access Member
- Joined
- May 25, 2012
- Posts
- 611
- Reaction score
- 222
- Location
- Central Coast, CA
- First Name
- Todd
- Truck Year
- 1990 w/307k miles on the clock
- Truck Model
- GMC V1500 Suburban SLE
- Engine Size
- 5.7L TBI/4L60/3.42's
Thought I'd post a little write up on an issue I've been having for about a year now.
About 18mos ago we were on a long trip to and from Sacramento, towing the popup camper in the heat. Basically 5hrs each way, in 90+ temps, with the front and rear a/c running.
Wound up with melted wiring connectors at the front blower fan, and discovered that the ground wire for the blower was too small, and poorly connected.
Upgraded the ground for the blower with some 2 gage battery ground cable with an eyelet at each end. Upgraded the power wire from the blower relay on the side of the evaporator housing down to the blower with some 8ga.
Thought that would take care of it, but I guess the failure got the rotary control in the HVAC control unit so hot that it melted the rotary control guts.
What I wound up with was a slide control that would barely shut the compressor off in the "off" position, and held the compressor on in the "vent" position.
On top of that, at random, there'd be a melting electrical smell, and recently, even smoke coming out of the center vent area.
Finally got off my lazy a$$ and tore into the problem yesterday:
-Remove instrument panel surround.
-Remove the 4 hex-head screws that hold the HVAC controller to the dash.
-Pull controller out far enough to rotate bulb holder 1/4 turn and pull out the back.
-Pull controller further out of the dash to gain access to the 2 screws that mount the rotary control to the main HVAC control assembly.
-Lift the rotary control straight up and off the main assembly.
Take apart the rotary control:
-Use a wide blade screwdriver to carefully pry the plastic "rivet/plug" out of the center of the rotary assembly. Just place the screwdriver under the round head of the rivet and pry, it'll let go and pop out.
-Lift off the rotary control housing cover:
Note the position of the 3 springs, and how they are clocked so you can put it back together in this position. This is the "off" position, and it's how you removed it, and how it'll go back into the main HVAC control assembly.
If you like electrical diagrams: power comes into the rotary switch via the right-most contact in my photo, and the curved distributes that power. That wire is solid brown. The connector to the left of that in the photo, is blank. The next connector to the left in the photo is what connects to the melted area, and that's a green wire. That green wire powers the a/c compressor by passing through the low pressure switch mounted to the receiver/dryer. The left-most connector in the photo takes 2 brown wires that have white stripes. These wires "arm" the blower speed switch, and turn on blower speed 1 as the default blower setting (low speed).
Note in the wiring diagram below that the green wire powers the a/c clutch directly, with no relay to carry the load of the compressor magnetic winding. It's no wonder the rotary switch gets hot. In fact, the compressor clutch failed not long after that big trip to Sacramento, so I guess now I'm starting to understand the entire picture.
Disassemble the rotary switch:
-Take the springs and the rotary contact plate off.
See where my plate was burned and where it was burning the plastic housing?
I ordered a good used HVAC controller on ebay for $20, but figured I would make an attempt at repairing this one. I cleaned all the grease up and dug the loose stuff out of the holes that had been melted into the plastic. Then I packed the holes with Epoxy Steel Putty:
Once cured, I sanded the putty repair areas flat, and trimmed the edges so they lined up with the actual edge of the brass contacts so that the off and on functions would be in the correct locations on the sliding lever.
With this repair complete, the HVAC controls were back functioning corrrectly again. However, there was still a question of why was it getting so hot. I took a look at my battery cable ground wire install and discovered that it was not very tight on the motor housing. I replaced the original screw with a much larger version and used a toothed washer for better grip.
So far, so good.
Here's a colored version of the GM wiring diagram that's been posted over in the library. Light green sends power from that middle burned up area of my switch, out to the a/c compressor, via the low pressure switch on the receiver/dryer. The light green leaves the receiver/dryer as dark green and goes to the compressor. From the compressor leaves a black ground wire.
I'm going to further investigate the ground wire at the compressor and probably wind up replacing it with something much larger. It think the existing ground wire is about 14ga. Ridiculous.
About 18mos ago we were on a long trip to and from Sacramento, towing the popup camper in the heat. Basically 5hrs each way, in 90+ temps, with the front and rear a/c running.
Wound up with melted wiring connectors at the front blower fan, and discovered that the ground wire for the blower was too small, and poorly connected.
Upgraded the ground for the blower with some 2 gage battery ground cable with an eyelet at each end. Upgraded the power wire from the blower relay on the side of the evaporator housing down to the blower with some 8ga.
Thought that would take care of it, but I guess the failure got the rotary control in the HVAC control unit so hot that it melted the rotary control guts.
What I wound up with was a slide control that would barely shut the compressor off in the "off" position, and held the compressor on in the "vent" position.
On top of that, at random, there'd be a melting electrical smell, and recently, even smoke coming out of the center vent area.
Finally got off my lazy a$$ and tore into the problem yesterday:
-Remove instrument panel surround.
-Remove the 4 hex-head screws that hold the HVAC controller to the dash.
-Pull controller out far enough to rotate bulb holder 1/4 turn and pull out the back.
-Pull controller further out of the dash to gain access to the 2 screws that mount the rotary control to the main HVAC control assembly.
-Lift the rotary control straight up and off the main assembly.
You must be registered for see images attach
Take apart the rotary control:
-Use a wide blade screwdriver to carefully pry the plastic "rivet/plug" out of the center of the rotary assembly. Just place the screwdriver under the round head of the rivet and pry, it'll let go and pop out.
-Lift off the rotary control housing cover:
You must be registered for see images attach
Note the position of the 3 springs, and how they are clocked so you can put it back together in this position. This is the "off" position, and it's how you removed it, and how it'll go back into the main HVAC control assembly.
If you like electrical diagrams: power comes into the rotary switch via the right-most contact in my photo, and the curved distributes that power. That wire is solid brown. The connector to the left of that in the photo, is blank. The next connector to the left in the photo is what connects to the melted area, and that's a green wire. That green wire powers the a/c compressor by passing through the low pressure switch mounted to the receiver/dryer. The left-most connector in the photo takes 2 brown wires that have white stripes. These wires "arm" the blower speed switch, and turn on blower speed 1 as the default blower setting (low speed).
Note in the wiring diagram below that the green wire powers the a/c clutch directly, with no relay to carry the load of the compressor magnetic winding. It's no wonder the rotary switch gets hot. In fact, the compressor clutch failed not long after that big trip to Sacramento, so I guess now I'm starting to understand the entire picture.
Disassemble the rotary switch:
-Take the springs and the rotary contact plate off.
You must be registered for see images attach
See where my plate was burned and where it was burning the plastic housing?
You must be registered for see images attach
You must be registered for see images attach
I ordered a good used HVAC controller on ebay for $20, but figured I would make an attempt at repairing this one. I cleaned all the grease up and dug the loose stuff out of the holes that had been melted into the plastic. Then I packed the holes with Epoxy Steel Putty:
You must be registered for see images attach
Once cured, I sanded the putty repair areas flat, and trimmed the edges so they lined up with the actual edge of the brass contacts so that the off and on functions would be in the correct locations on the sliding lever.
With this repair complete, the HVAC controls were back functioning corrrectly again. However, there was still a question of why was it getting so hot. I took a look at my battery cable ground wire install and discovered that it was not very tight on the motor housing. I replaced the original screw with a much larger version and used a toothed washer for better grip.
So far, so good.
Here's a colored version of the GM wiring diagram that's been posted over in the library. Light green sends power from that middle burned up area of my switch, out to the a/c compressor, via the low pressure switch on the receiver/dryer. The light green leaves the receiver/dryer as dark green and goes to the compressor. From the compressor leaves a black ground wire.
I'm going to further investigate the ground wire at the compressor and probably wind up replacing it with something much larger. It think the existing ground wire is about 14ga. Ridiculous.
You must be registered for see images attach
Last edited:
