Hey guys,
Truck: 1992 GMC Sonoma, 4.3L TBI, 4WD, with A/C.
I’m chasing the classic HVAC issue (air only blows from defrost). I found the black hard plastic vacuum line from the firewall that had ~15 inHg vacuum engine side. I pulled it to figure out where it’s supposed to go as I checked if there was vacuum at lines on control and only grey was putting out vacuum. So I assumed the black line was not plugged in anywhere and now I can’t figure out how to get it back in place. Does the black hose from firewall connect to grey hose? I saw a video on youtube of someone taking apart a dash and saw a grey hose in same place where black would come in from firewall and it looked like it had same fitting and connection.
Here’s what I’m seeing:
Thanks in advance , any pics of your harness would help a ton.
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Truck: 1992 GMC Sonoma, 4.3L TBI, 4WD, with A/C.
I’m chasing the classic HVAC issue (air only blows from defrost). I found the black hard plastic vacuum line from the firewall that had ~15 inHg vacuum engine side. I pulled it to figure out where it’s supposed to go as I checked if there was vacuum at lines on control and only grey was putting out vacuum. So I assumed the black line was not plugged in anywhere and now I can’t figure out how to get it back in place. Does the black hose from firewall connect to grey hose? I saw a video on youtube of someone taking apart a dash and saw a grey hose in same place where black would come in from firewall and it looked like it had same fitting and connection.
Here’s what I’m seeing:
- My vacuum harness block behind the control head has orange, blue, gray (I think goes to an actuator), brown, and black hoses going out to actuators.
- There is no open nipple anywhere on the block that looks like it’s meant for the firewall hose.
- There is a stub that looks like a nipple, same size as the others, but it’s molded closed.
- Before I pulled it, the firewall line had been connected into I believe the gray line which gave me constant defrost vacuum but nothing else.
- Now I’ve got a loose firewall hose under the hood and a vacuum leak, and I can’t drive until I figure out where this thing really goes.
- On your harness, where does the firewall vacuum line plug in? Is there a true black supply nipple on the block, or does it splice into the black hose already in the harness?
- Is the “sealed” nipple on mine supposed to actually be open, and mine’s broken/blocked?
- Does anyone have a clear picture of the correct harness routing for a 1992 truck?
Thanks in advance , any pics of your harness would help a ton.
