1992 Peterbilt 379 HVAC system actuators and switches

CCW-Truck · Sep 13, 2021

H2oburymatt said: ↑

Need a little help determining what this part is exactly and where to get one. I'll start by saying when I purchased this Pete about a year ago the AC in the cab blew ice cold. This winter it stopped working at some point and when the warmer weather rolled around I no longer had any ac at all. The controls had to be set to bi level or floor in order to not have air leaking behind the dash. I found where a fitting was bad in an AC line under the hood, replaced it, pressure tested it. Replaced the dryer. Recharged it and it blows ice cold again It's converted to 134-a from r12 being as old as it is and that was done before I got it. I start fixing the air leaks behind dash and quickly realize both actuators are bad and leaking. I order part DA 10000 and DA 10050. The first number is for the dual action actuator and second number is for the single action actuator. Once I replace those I am getting a leak from the male branch tee that's screwed into what looks like a block of some sort that also has what I think is a low pressure switch or binary switch?? Screwed into it as well. Please reference the picture for actuators and switch. The switch has 2 prongs and an electric wire to each and male thread screwed into the same block as the male tee branch that swivels and is in line with the single action actuator. This system is all controlled with air. The tee is what's actually leaking where one of the lines goes into the quick connect. The switch may be good but im afraid once I disconnect the tee or get proper air flow to it that it'll possibly fail as well and I want to replace it all while im in there anyway. Peterbilt said that it's probably the low pressure switch and if so it's discontinued.
My questions are is it a binary switch or low pressure switch? Are they different? What purpose does this switch serve? Do the controls and actuators run off of the 120psi in the truck or is it stepped down somewhere to run at lower psi? Does anyone know what size air line that Peterbilt used in 1992 for the air controls pictured? And where do I get a new assembly with switch and block and tee if possible lol?! Probably a long shot. View attachment 232607 View attachment 232608 View attachment 232602
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The"assembly" your fingers are pointing at isn't really an assembly at all -- just a plastic quick-connect tee screwed into a brass 90-degree elbow, with the low air warning switch screwed into it. The switches are available from Kenworth with a 70 psi set point -- they're standard 1/4" air switches. After I bought my 1994 Pete 377 I had to buy 2 of them. Mine were in a common aluminum air manifold on the floor behind the clutch pedal.

Flexedbmw · Feb 23, 2022

Does anyone know how to switch it all to electric and get rid of all the air actuators? I've been thinking of taking the whole electric ac/heat control off one in a junkyard. I'm tired of the air leaks and not being able to get the correct part due to covid.

Diesel Dave · Feb 24, 2022

Flexedbmw said: ↑

Does anyone know how to switch it all to electric and get rid of all the air actuators? I've been thinking of taking the whole electric ac/heat control off one in a junkyard. I'm tired of the air leaks and not being able to get the correct part due to covid.
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@staceydude

Flexedbmw · Feb 24, 2022

Diesel Dave said: ↑

@staceydude
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Woodrow84 · Mar 25, 2023

H2oburymatt said: ↑

View attachment 232603
Peterbilt gave me Rd3-4084-1 for the discontinued part number for the "low pressure switch"
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Where exactly are these located.

Ngardner96 · May 1, 2024

RocketScott said: ↑

Sorry I'm a little late, been on vacation. Thought I should contribute what I know in case you haven't fixed it or someone else comes looking.

The RD in that part number stands for Red Dot. They made the Hvac system. Sometimes you'll get better results searching for parts if you put a dash between the RD and the rest of the part number or searching Red Dot and the number. Sometimes taking all the dashes out works. If you take the cover below the glove compartment off there might be a schematic for the system inside. There was one in my '89 anyway.

The part number for the white actuator is RD-5-5784-2 and the red actuator is RD-5-5784-3 going off the schematic that the Peterbilt dealer printed off for me (I think they got tired of me standing at the parts counter trying to figure things out). It's a little confusing because the schematic shows two different air distribution boxes but the parts list doesn't have details for the other one. I'm guessing the other is for heat only, no AC, and my truck has AC. Just a guess. The schematic that was in my truck shows the same part number for both those cylinders but it's hard to read. RD-5-54*4-4. The * might be a 5, not sure.

The part number RD-3-4084-1 they gave you for the switch is correct by my information from Peterbilt but I believe is only for the switch itself, even though it says 'assembly' in the parts list. It's a normally open switch. I believe the current part number is RD-5-5538-0P or 72R0070.

The fitting it goes into is RD-5-5548-0. Unless it's cracked you should still be able to use it. That T fitting should be easy to find from other sources. It's 3/16 air hose. I think the thread is 1/8" NPT but better check it to make sure.

Here is the Red Dot catalog:

2017 Red Dot Aftermarket Catalog
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can i get a picture of your schematic. I am putting together an 88 peterbilt that i didnt take apart. And i have everything done beside the Hvac system. And i seem to cant find a decent schematic for it.

RocketScott · May 2, 2024

Ngardner96 said: ↑

can i get a picture of your schematic. I am putting together an 88 peterbilt that i didnt take apart. And i have everything done beside the Hvac system. And i seem to cant find a decent schematic for it.
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These are the schematics that were behind the housing cover in the truck. I'll get the schematic that Peterbilt gave me scanned in and post when I can. It's almost identical but has more recent part numbers

OK, I give up. Can't seem to post pictures from Imgur. Send me your email in a private /direct message and I'll send them to you

Diesel Dave · May 2, 2024

@staceydude might be able to help.

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