BJ74 13bt A/C question (1 Viewer)

[SeanBJ74]

So last week I put a brand new ac compressor in the BJ74 and my mechanic installed it and fully charged the compressor but told me the electrical from compressor to the cab either needs to be repaired or replaced as it was not working. Has anyone had this issue? Took it to a couple other AC shops around town and a lot of people are scared to work on the truck. Has anybody had this electrical issue ?
1986 BJ74, 13bt, RHD, auto

 

[RhinoRig]

Yes. Your best bet is to learn your system intimately so you can tell them what needs done. It’s a simple system really that requires an on switch (manual or thermostat) and a pressure switch (lack of pressure protects the compressor) that closes the relay that sends power to the compressor. Of course it’s not that simple but that’s the concept. Get a wiring diagram and check that it’s right/make corrections based on the existing. You should at least be able to hot wire the compressor and make sure the clutch engages and it spins. If it’s charged, you should get cold.

 

[jblueridge]

On mine it all came down to the black plastic box behind the glove box.
It holds a circuit board and relay that sends power to the ac clutch.
When that stuff failed, I wired in a bypass to the compressor clutch.
I flip a switch on the dash and I get ac.
I cycle it on and off as I drive.
Far less than perfect but better than death by heat.

If you or anyone else can describe exactly how the black box works, please let me know.

 

[SeanBJ74]

On mine it all came down to the black plastic box behind the glove box.
It holds a circuit board and relay that sends power to the ac clutch.
When that stuff failed, I wired in a bypass to the compressor clutch.
I flip a switch on the dash and I get ac.
I cycle it on and off as I drive.
Far less than perfect but better than death by heat.

If you or anyone else can describe exactly how the black box works, please let me know.

So you wired a switch straight from the ac clutch to your dash ? No fuses or anything ?

 

[Felde]

In general I agree with RhinoRag.
Of course wiring however should be done professionally: Put fuses and drive the working power for the compressor by a relay rather than running it straight over a switch. Get the pressure switch in line, too.
The old A/C system are not sensor controlled. When On, they produce cold. Lots of it.
It must be assured a) this cold is moved out of the system into the passenger room. If not, ice will build up and crack the vent.
Also, b) when the engine is off, the compressor would drain the battery in no time.
To overcome these topics, the original wiring board only provides power to switch the A/C on, when a) the fan is operating, which b) only works when ignition is engaged.
So, in essence, you have three switches in line engaging the relay to switch the compressor (Fan on, pressure switch, A/C on, relay).

 

[Felde]

So last week I put a brand new ac compressor in the BJ74 and my mechanic installed it and fully charged the compressor but told me the electrical from compressor to the cab either needs to be repaired or replaced as it was not working. Has anyone had this issue? Took it to a couple other AC shops around town and a lot of people are scared to work on the truck. Has anybody had this electrical issue ?
1986 BJ74, 13bt, RHD, auto

I only read your initial question now. Sorry.
Are you (and your mechanic) aware of the fan thst need to be turned on as a prerequisite for the AC to work in the factory setup?
Might be the trick...
Regards Ralf

 

[jblueridge]

So you wired a switch straight from the ac clutch to your dash ? No fuses or anything

I added a fuse with a so-called Fuse Tap.
fuse tap

No relay, so I guess I could be electrocuted when I touch the switch.
My RHD dash has a hole to the left of steering column that once held a fog light switch.
So wire runs from fuse box to dash switch then through firewall via right side factory rubber grommet and on down to the compressor. I used corrugated plastic sleeving to protect the wire in the engine bay.
sleeve
I connected to the compressor clutch with a crimp-on quick disconnect terminal.

I did all this crap with stuff I bought at an Advance Auto store in WV. It was do or die for my vacation as I was not going to drive cross country in July with no ac.

 

[SeanBJ74]

I added a fuse with a so-called Fuse Tap.
fuse tap

No relay, so I guess I could be electrocuted when I touch the switch.
My RHD dash has a hole to the left of steering column that once held a fog light switch.
So wire runs from fuse box to dash switch then through firewall via right side factory rubber grommet and on down to the compressor. I used corrugated plastic sleeving to protect the wire in the engine bay.
sleeve
I connected to the compressor clutch with a crimp-on quick disconnect terminal.

I did all this crap with stuff I bought at an Advance Auto store in WV. It was do or die for my vacation as I was not going to drive cross country in July with no ac.

Yea man that’s sounding like my best bet right about now. This Miami heat is no joke in the summer time. Thanks for explanation brother!

 

[pithicus]

Maybe they fitted a compressor with a 24v clutch. If your bj is 12v that could be a problem.

 

[SeanBJ74]

Does anybody know where the pressure switch is on the BJ74 a/c compressor or if there is one

 

[pithicus]

Does anybody know where the pressure switch is on the BJ74 a/c compressor or if there is one

Screwed in on the evaporator ,not the compressor, I would assume. That's where fj73's and 60- 62's are.

 

[jblueridge]

Yes. It is in the evaporator housing which is inside the cab. On my rhd BJ74 it is just above passengers feet inside the plastic housing.