A/C Condenser Fan

1998_K1500_Sub

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In my 1990, there was a single wire cut-out on the back of the original compressor that I had to change to 2 wire when converting to R-134, which I think had a similar function to the later systems. On my 92, no such switch is present (and there is no wiring for it either). Wiring manuals for both years match up with this reality. No switches are present at all on the condenser output on either. I think that the recirculate function is controlled by this switch in the 1990. When turning on the AC, it will blow for about 20-30 seconds, then you can hear the air start to recirculate. Since the recirculate option was added to the control head in 92, this was likely the reason for dropping the switch in that year (although the compressor is the same and just has a plug in place of it). When trying to source lines for the 1990 truck (NOT easy for a 454 since they have a unique mounting orientation and high side valve location), the only two that I could find were for 92 and 94, and the pictures did look like the 94 had an additional port like you mentioned.

Both trucks have the auxiliary cooling fan as well, and the wiring looks identical. Power is wired directly from the power block with a fusible link to the relay, ignition power is sent to the other contact, and ground is provided through the switch in the head. Simple! The 1994 AC controller and ecm seem pretty similar to earlier models, despite the switch to R-134, so it seems unlikely that the operation of the fan would be completely different (especially if it involved making special wiring accommodations just for 454 trucks). Now, 95 is an oddball in all directions, so I'm not so sure on that one, and I can't find a 95 wiring manual to study this. When inclusion of the cooling fan expanded beyond big blocks, along with improved computer functionality, it makes sense to make more efficient use of the auxiliary fan.

Thanks for the detailed summary, I’ll study it and follow up with questions.
 
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Thanks for the help, guys! I've been thinking about getting a programmer from Banks, Bullydog, et cetera anyway. Now that I know I can control the auxiliary fan from the ECU and the programmers allow you to lower the temperature to when the auxiliary fan kicks on, I may give this a try.

No one really gave opinions about changing the stock auxiliary fan with "beef-ier" twin fans. The oversized radiator, heavy duty water pump, and oil cooler seem to keep the 454 running remarkably "cool." Thoughts on that?
 

PlayingWithTBI

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Ask @PlayingWithTBI about the time his system blew a hose on the high-side after hot start-up and it dumped the contents of the AC system (oil and refrigerant) into his engine bay.
Even worse, it blew the high pressure switch out of the back of the compressor (sounded like a shotgun going off in my lap), which tore the snap ring groove rendering the compressor useless, except for an almost brand new clutch and pulley set up, ha ha.

Note: that was before I wired the high pressure shut off switch in parallel with the low pressure cycling switch.
 

PlayingWithTBI

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In my 1990, there was a single wire cut-out on the back of the original compressor that I had to change to 2 wire when converting to R-134, which I think had a similar function to the later systems.
No, that 1-wire switch (since discontinued by GM) was only for closing your recirculation door when high pressures exist on an R12 system which never saw as high pressures as R134A. That's why I wired the 2 wire switch in parallel (see previous post).
 

PlayingWithTBI

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Since the recirculate option was added to the control head in 92, this was likely the reason for dropping the switch in that year (although the compressor is the same and just has a plug in place of it).
I'm guessing you need to install a HP switch there and find the wires that go to it. Otherwise you don't have any safety provisions for a hot restart when pressures will go over 500 PSI. R4 compressors don't come with a switch on the back, that's up to the buyer and their particular application.
 

packer0440

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I'm guessing you need to install a HP switch there and find the wires that go to it. Otherwise you don't have any safety provisions for a hot restart when pressures will go over 500 PSI. R4 compressors don't come with a switch on the back, that's up to the buyer and their particular application.
I figured that one wire switch did that, forgot to delete the other part. I may end up wiring a switch on the 92, but as it stands there are no factory wires for it that I can see. The wiring diagram for 92 doesn’t show any high pressure cut out wires either. Although, I am pretty blind when it comes to finding things, I’ll probably have another look sometime.
 

packer0440

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Thanks for the help, guys! I've been thinking about getting a programmer from Banks, Bullydog, et cetera anyway. Now that I know I can control the auxiliary fan from the ECU and the programmers allow you to lower the temperature to when the auxiliary fan kicks on, I may give this a try.

No one really gave opinions about changing the stock auxiliary fan with "beef-ier" twin fans. The oversized radiator, heavy duty water pump, and oil cooler seem to keep the 454 running remarkably "cool." Thoughts on that?
I don’t really see the need barring extreme heavy duty work. A mechanical fan, especially the 10(?) blade one that will bolt in on a big block and fit (others may chime in that know more about this), will cool better than most electric setups. It just robs a little bit of power. Upgrading the electric fans might net a little better AC performance, but personally I wouldn’t think it would be worth the struggle.
 
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