(Another) Electrical short -- A/C - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**ThreeQuarter** · 09-08-2002, 05:55 PM

There's a problem with the factory A/C system in my friend's '68. When I turn it on, the whole system shuts down, like it blew a fuse (blower motor, compressor clutch, everything just turns off). And I can switch it on and off after that and it's just dead. But I can unhook the battery and hook it back up, and then when I turn the system on I get the quick burst of electricity and then the "blown fuse" type thing again. Is there some kind of breaker that can be thrown in this system? I eralize it has a short some where but I am curious of how it resets.

I'm clueless on this one, and don't need to be tearing into the A/C electricals. Thanks in advance for any help.

*Zkast* · 09-08-2002, 06:21 PM

I think you almost on the right track.. Check the fuse where the contacts meet the fuse itself. If they are dirty or correded you will lose power under high load.

**1970 CST Short Wide** · 09-08-2002, 08:51 PM

The same thing happened to my truck. WAY up in the ducting there is a relay. Hard to explain but its in what I'll call the heater box, you have to take the plastic box apart (screws) and look up inside. After I changed this it works perfect. I got the new switch from the Truck Shop. You might find a picture in LMC maybe.

Hope this helps, I know it not a good discription

mtdave2 · 09-08-2002, 08:58 PM

might sound strange, but check all your grounds first. everytime i have had a strange electrical prob. is been a ground.

**ThreeQuarter** · 09-08-2002, 11:56 PM

Gosh, there's got to be many grounds in that system. I wouldn't know where to start.

I can't even get the system to even blink anymore. I'll try the relay first--thanks 1970CST.

Other than that, I think his fuse box is shot. Has a leak in the cowl right above it and I tried to clean and patch it with body seam sealer but to no avail. This is getting hairy.

O'l Buck · 09-09-2002, 12:02 AM

according to my automotive electrical instructor in college, "the most overlooked portion of the electrical circuit is the ground" it's probably a connection somewhere that isn't making good contact, you can "hotwire" the clutch and see if it engages and whether or not it warms up the wire you ran to it, other than that, the only thing that should draw any current should be the blower motor, or possibly the relay mentioned above is grounding and drawing too many amps.

**ThreeQuarter** · 09-10-2002, 09:48 PM

Quote:

Originally posted by 1970 CST Short Wide
WAY up in the ducting there is a relay.

You talking about the blower motor rheostat? The one that is the resistor for the three fan speed circuits? It is a little fiberglass plate with either two or three (can't remember which) wire coils attached to one side. Is that what you're talking about?

**ThreeQuarter** · 09-13-2002, 03:01 PM

ttt

09-08-2002, 05:55 PM	#1
ThreeQuarter Senior Member Join Date: Jun 2000 Location: Texan in Iowa Posts: 2,522	(Another) Electrical short -- A/C There's a problem with the factory A/C system in my friend's '68. When I turn it on, the whole system shuts down, like it blew a fuse (blower motor, compressor clutch, everything just turns off). And I can switch it on and off after that and it's just dead. But I can unhook the battery and hook it back up, and then when I turn the system on I get the quick burst of electricity and then the "blown fuse" type thing again. Is there some kind of breaker that can be thrown in this system? I eralize it has a short some where but I am curious of how it resets. I'm clueless on this one, and don't need to be tearing into the A/C electricals. Thanks in advance for any help. __________________ Ben '68 Chevy C10 Custom LWB 327/TH400 2nd owner '16 GMC Sierra 1500 SLE Dblcab 4wd 5.3

09-08-2002, 08:51 PM	#3
1970 CST Short Wide Senior Moment Join Date: Mar 2002 Location: Pittsburg Ca Posts: 4,107	The same thing happened to my truck. WAY up in the ducting there is a relay. Hard to explain but its in what I'll call the heater box, you have to take the plastic box apart (screws) and look up inside. After I changed this it works perfect. I got the new switch from the Truck Shop. You might find a picture in LMC maybe. Hope this helps, I know it not a good discription __________________ 1970 CST LS 1 6 speed Ford 9 inch Detroit Tru Track, Dakota Didgital, Vintage Air, QA1 Coil Overs Front & Rear Lots of FUN 2013 GMC PU, Oldest Son 71 GMC LWB. QA1 Suspension, Angry SB. Youngest Son 2019 GMC Diesil Dually. Youngest Son 2017 Toyota SUV Daughters car 2018 Traverse , Wife’s Ride Pittsburg Ca 94565

09-08-2002, 08:58 PM	#4
mtdave2 newly minted old timer Join Date: Dec 1999 Location: Hudson WI Posts: 3,508	might sound strange, but check all your grounds first. everytime i have had a strange electrical prob. is been a ground. __________________ ____________________________________________ 72 c20 longhorn 65k org miles and counting! 69 k10 Suburban

09-08-2002, 11:56 PM	#5
ThreeQuarter Senior Member Join Date: Jun 2000 Location: Texan in Iowa Posts: 2,522	Gosh, there's got to be many grounds in that system. I wouldn't know where to start. I can't even get the system to even blink anymore. I'll try the relay first--thanks 1970CST. Other than that, I think his fuse box is shot. Has a leak in the cowl right above it and I tried to clean and patch it with body seam sealer but to no avail. This is getting hairy. __________________ Ben '68 Chevy C10 Custom LWB 327/TH400 2nd owner '16 GMC Sierra 1500 SLE Dblcab 4wd 5.3

09-09-2002, 12:02 AM	#6
O'l Buck Recovering Truck Driver Join Date: Mar 2002 Location: Orleans, NE USA Posts: 1,883	according to my automotive electrical instructor in college, "the most overlooked portion of the electrical circuit is the ground" it's probably a connection somewhere that isn't making good contact, you can "hotwire" the clutch and see if it engages and whether or not it warms up the wire you ran to it, other than that, the only thing that should draw any current should be the blower motor, or possibly the relay mentioned above is grounding and drawing too many amps. __________________ 67 K-20 350, SM465, Eaton rear, 4.56 no spin option 00 Dodge 2500 4x4, 24V cummins, 5 speed Chad South Central Nebraska

09-08-2002, 06:21 PM	#2
Zkast Account Suspended Join Date: May 2002 Location: Olathe, Kansas Posts: 929	I think you almost on the right track.. Check the fuse where the contacts meet the fuse itself. If they are dirty or correded you will lose power under high load.

09-13-2002, 03:01 PM	#8
ThreeQuarter Senior Member Join Date: Jun 2000 Location: Texan in Iowa Posts: 2,522	ttt __________________ Ben '68 Chevy C10 Custom LWB 327/TH400 2nd owner '16 GMC Sierra 1500 SLE Dblcab 4wd 5.3



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