A/C and blowing fuses

[82ChevyC10b]

I have a 1982 Chevy C10 pickup with the straight-6 engine and a mostly operational A/C system. The A/C-heater regulator is an aftermarket model, purchased several years ago from   Truck. The A/C system worked up until about nine months ago, when it suddenly stopped working. After a brief investigation, I discovered that the 20-amp blade fuse blows whenever the regulator is switched to cooling or defrosting. With a good fuse, the heating and venting operations work fine.

What do I have here — a short or ground problem at the regulator or somewhere under the hood? What's the next step in the problem solving?

Thanks.

[VileZambonie]

AC heater regulator? Not sure what that is but:

Mode Control = Defrost, Vent, Floor

Blend Control = Hot/Cold Mix

and then you have the Blower Fan Speed. Can you elaborate on what system you have? Pix? Is it Vintage Air? From what I got out of your post, when the AC compressor is engaged the fuse blows. If that's the case, unplug the compressor power wire and see if it still happens.

[JohnnyPopper]

Nomenclature, of the accurate type, is a wonderful thing 

[82ChevyC10b]

"A/C-heater regulator"? The A/C-heater-fan controls above the radio. The classic (original) style for the '82 Chevy C10. The only big A/C change since I've had the truck — I bought it during the summer 1999 — was the switch to the newer refrigerant. Thanks.

[JohnnyPopper]

Don't mean to frustrate you 

If your control system is stock, or like it, there are 3 levels of controls, right?

Fan speed

Mode: Air Conditioning,  Vent, Defrost.

Heat Regulator: Slide from cold to hot regardless of what mode you're in.

So help us out here by identifying what makes sense for you, Okay?

[82ChevyC10b]

It's the stock style, though not the original control box. Four fan speeds with the up-and-down lever on the left — LO at the bottom and HI at the top. Left-to-right mode controls on the top row with groups of AIR COND (MAX, NORM and BI-LEVEL), ECONOMY (VENT and HEATER) and DEF. Left-to-right heat regulator on the bottom, going from COLD on the left to HOT on the right. If the system is on VENT or HEATER with a good 20-amp blade fuse, the fuse blows when I move the mode control to the left (to BI-LEVEL) to kick in the A/C system or to the right to activate DEF. Basically, the fuse blows whenever the compressor is activated.

[bd]

Did you ...

unplug the compressor power wire and see if it still happens.

                  ??

[82ChevyC10b]

I'll follow through with your suggestion this weekend — with the work week behind me. I have a sense the fuse won't blow when the compressor power wire is unplugged. Thanks.

[82ChevyC10b]

OK, I tried the A/C controls with the wire connector detached from the compressor. The fuse blew again when I switched the lever from VENT to AIR COND. What's next with the troubleshooting? Thanks.

[JohnnyPopper]

Something is grounding. Look for a damaged wire, the main wire with the most exposure is the green one going to your compressor.

Is there a time marker that you can point to when this began? Was there work done at that time?

[82ChevyC10b]

Thanks. I'll look for a wiring problem. There's been one suggestion that a ground/short fault might be between the A/C controls and the fuse box. I'll look there, too. As for the time marker, I actually noticed the problem mid-winter, when I was moving the controls to get some heat. I noticed I wasn't getting any air from the vents. After a while, I figured out that that going to A/C or DEF with the horizontal mode lever was blowing the fuse. It wasn't a service-related issue.

[bd]

Unplug the idle solenoid on the carburetor and recheck for blowing the fuse.

[frotosride]

Also check the AC compressor itself. Two steps one is a little more involved.
1) check the coil to ground... Unplug the harness from the compressor, set your multimeter to resistance and verify there's infinite resistance from each of the contact leads coming from the compressor to a verified good ground. This is a simple electromagnetic and if the windings have burned they can ground on the housing causing an overload condition.
2) check the compressor for binding... Without the Engine or key on attempt to turn the center portion of the compressor (not the pulley on the outside) the compressor should move with some resistance in the clockwise rotation only. If it doesn't move or feels like it's binding the compressor is bad.
Last one, 3) Typically the blower fan is powered through the same circuit. If the blower fan resistor is bad or going bad the extra load for the blend door actuator or AC compressor, could cause over current and blow the fuse. Also a faulty blend door actuator could cause a grounding and or over current condition resulting in a blown fuse.

[VileZambonie]

If he unplugs the AC compressor clutch and it still blows the fuse, there is no need to investigate the compressor. There is no blend door actuator, it is cable operated, you don't want to send him down a rabbit hole.

Go to the idle solenoid next and disconnect it, then report.