1
« Last post by Happytexan on July 12, 2025, 11:31:03 pm »
Wow! Thank you! The blower does run all of the time with key on. Have been told before that it’s to keep fresh air in the cab to combat CO from accumulating. Thank you for explaining the thermostatic switch. I was wondering what that is. The trucks I’ve had experience with have all been 77-79 models. It’s interesting to see the progression made in this body style. The other issue I’m trying to figure out is why the idle mixture screws on the q-jet do nothing. Found the carb mount gasket bad, good size vacuum leak. Replaced it with a new fel-pro gasket. Have capped off all of the vacuum ports on the carb accept the booster and vacuum advance. Put new hose on those. Need to cap off the intake manifold vacuum outlets for the trans and hvac to eliminate those possible sources as well. With the mixture screws in, I can turn the idle down 550 rpm and it purrs just fine. I backed the idle screw a half turn past the point of the engine dying to see if the blades were past the proper transfer slot alignment. Turned the screws out 2 full turns each and it made 0 difference. No start/no idle.
2
« Last post by 1981lt1 on July 12, 2025, 12:06:52 pm »
Don't even fiddle with those gaps til you are sitting on your good body mounts.
Yup. Got some bushing parts on order since I don't quite trust the original bolts and washers.
3
74 is a different system that uses a thermostatic switch which you can see in the engine bay side of the evaporator case and a high side pressure switch in the liquid line. Later models just used a low pressure switch at the accumulator. Low 2 Mediums & High are your only options for fan speed with technically no fan off option. Key on it should come on and run at whichever speed the selector is at. The ground wire should jump off the blower housing and to the firewall. When the blower stops working you need to be ready to pinpoint where it is dropping out and why. It sounds like you could have compounded issues, so I would address them one at a time.
4
« Last post by Happytexan on July 12, 2025, 12:57:30 am »
I followed your t/s instructions and found the fuse had been replaced with a breaker by the PO. All connections good, ground is good. My first truck I had almost 30 years ago was a 78 big 10 camper special with a 400 small block. Being a 78, that truck had different a/c modes. The 74 I now have only has one a/c option. No max option. So when you put the mode switch on a/c, it switches the blower to high speed, the same way my old 78 did on max a/c. If I switch it to bilevel, then all 4 blower speeds work as they should. This now has me wondering if the later hvac controller with multi a/c settings will work in my 74. Thanks again for the help and tech info.
5
Don't even fiddle with those gaps til you are sitting on your good body mounts.
6
I bought two from National, one for my daily and one for a project.
Daily wouldn't adjust on idle screws, turned in completely and the engine still ran.
Sent it back and they fixed it at no cost, even thought just out of warranty.
Replaced the throttle body and some other items.
If they don't have a carb to match what you have, they will rebuild yours. Good outfit!!
7
Ok, thanks! Mine is all clear, I removed and cleaned. Just one of those little things one doesn't deal with often.
8
I bought a QJ/Rochester from National Carb. VZ installed and tuned it (with a new engine), haven't touched it since, going on like 8 or 9 years. Gripe! ....has it been that long?! https://nationalcarburetors.com/
9
« Last post by 1981lt1 on July 10, 2025, 07:16:09 pm »
I haven't replaced the body bushings yet but the fender gap looks pretty good. I gotta do something about the A-pillar to door gap right above the fender though. It's pretty nasty.  
10
Temu 
|
1
Recent Posts