1988 Suburban Blower motor issues

CarolinaHD

CarolinaHD

Well-Known Member ?
Joined
Dec 2, 2008
Location
Gold Hill
1988 r2500 suburban 454 tbi 95k miles.
The tbi was running rough and needed to be rebuilt so I swapped in a fitech efi conversion.

The swap works great no issues there but now the front hvac isn't working. I've hooked up 12v to the blower and it runs so I know it's good.

I have the wiring diagram and from what i have read online I need to ground the dark green wire (59). I cut the wire before it goes into the ecm and grounded it and still doesn't work. I've given it 12v and blew the fuse... replaced it and still doesn't work.

Anyone done a carb swap or motor swap on an old tbi and how did you get the AC running?? Help please

20180101_163548.jpg
 
Found a diagram from the earlier trucks before they had computers.. looks like cutting the green wire from the ecm would make mine work but it doesn't..

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Grounding the dark green wire is not what you want to do according to the first schematic. There's two terminals on the compressor clutch, and one terminal is already grounded. If you ground the dark green wire, you're grounding both terminals, so there's no way that the compressor clutch can turn on. If this is like many vehicles, the ECU has the ability to disable the compressor during full throttle or during certain fault conditions, so it would stand to reason that the ECU is likely grounding the dark green wire under those conditions (to disable the compressor). If the dark green wire had anything to do with your problem, the blower would be running but the compressor would be the issue. It doesn't sound like the blower is running, so the problem is in a different area than the dark green wire.

Acutally, I take that back. There doesn't appear to be anything to limit current on the dark green wire if the ECU grounds it, so it's likely that the ECU is able to apply power instead. Don't know why the ECU would need to turn the compressor on instead of turning it off, but I'm just going off of what I see on the schematic. Could be missing something on that one.

Power comes from the brown wire, and power is connected to the compressor clutch wire in the MAX/NORM/BILEV/DEFROST positions.


I'm not familiar with the EFI swap you're doing, or what's required to get things running, but I'm picking it apart with the schematic.

I'm still digesting what would be needed here.

So what's the rest of the story here; what's actually working and what's not working? It sounds like it was all working before the EFI swap?
 
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So there's only two sources of power on that schematic. One is the red wire from the junction block that supplies power to the blower on high, and the other is the brown wire from the fuse block that supplies power to everything else and also to the blower on everything but high (through the resistor pack).

Do you have power on both of those wires? That's the absolute first thing I would check, because you have nothing without power on that brown wire.

Also, what was involved in the conversion? Did you remove and reinstall any harnesses or components that may now have a ground that's not connected? Always best to check the easy stuff first.

I'll be completely honest, this should have nothing to do with the EFI swap, because there is exactly one wire that connects to the old ECU and it only affects the compressor clutch and no other part of the HVAC system (like the blower, etc). The dark green wire may need to be disconnected from the old ECU connector for the A/C to work, but I don't know the details of that new ECU and whether it has the same capability for the full-throttle A/C compressor cutout. Either way, nothing you've touched should affect any function of the blower, etc., unless you've reinstalled something incorrectly or tapped into a wire that you shouldn't have.
 
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Thanks for the help, I think I got too hung up on the green wire.. anyways it's disconnected like it should be.

The efi conversion is by Fitech and is a self contained, self learning, throttle body unit. Nothing besides the obvious had to physically be removed for the swap, just needed a hei distributor.

Go Street EFI 400 HP – FiTech Fuel Injection

I do have power to the red junction block, I checked last night. I was up under the dash tracing wires and found a cluster of wire taps and nuts behind the radio. I removed the radio and the wiring and remember seeing a brown wire that was cut and didn't go with the rest of the radio wires. That's probably it.


Here's the timeline of the issue

Finished swap, everything worked fine but never tested the hvac
Noticed it wasn't working and found the rats nest behind the radio
Removed ratsnest wires and then cut the green wire after the fact
Still no hvac


So, I think, the ecm was keeping the ac from running via the dark green wire and I cut that wire after removing the spliced brown power wire. I'll know forsure this afternoon, thanks @Fabrik8!
 
Yep, that disconnected brown wire is the likely suspect. If that's the brown wire in the schematic, you will have no HVAC functions without it.

Older cars are fun. They're so simple compared to everything made in the last 20-25 years.
 
Ugh shoulda known that wasn't the issue, traced the brown wire to the fuse panel and it's all good. Checked the 2 prongs of the heater/ac fuse and only got 6.5 volts with key on... now what lol
 
You should have 12V between the battery side of the fuse and ground, if the fuse is not plugged in. If the fuse is plugged in, you should have 12V between the fuse terminals and ground.

Measuring between the two fuse terminals without the fuse plugged in doesn't tell you anything useful. You need a proper ground reference for the voltmeter.

Maybe I'm not understanding what you're saying...
 
If you have 12v between two test prongs (tabs on back) on a fuse that is plugged in the fuse is blown
 
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