Defrost problems 87 R2500 7.4 liter - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Black872500 · 11-26-2003, 08:51 PM

When I switch to defrost, it barely blows out the defroster vents and blows mosltly out the front dash vents. I located the vacuum switch by the tranny hump and it appears to be working. Must be another one up top somewhere?? Don't have a book on this truck.
Any help would be appreciated. The truck is a 1987 bigblock with AC. Thanks,

Greg

**old Rusty C10** · 11-26-2003, 09:05 PM

check right behind the switches sometimes vaccum there screws up

Grim Reaper · 11-27-2003, 03:06 PM

The vacuum deal you found is for the floor vents. The one for the defrost is behind the box. Take the glove box door off. That will give you access to the top of the box. Might have to drop the ECM. What you will see is the Diverter control cable for the temp slide. Almost directly behind that is the vack pot for the difroster flap. You should be able to feel the vac line.

Also make sure the Vac is connected under the hood. Factory the vac is connected to a "T" in front of the distributor. Yous should have a Vacuum ball, Check valve and then go into the truck.

Black872500 · 11-28-2003, 04:29 AM

Thanks, I'll give it a look.

Greg

11-26-2003, 08:51 PM	#1
Black872500 Registered User Join Date: Nov 2003 Posts: 7	Defrost problems 87 R2500 7.4 liter When I switch to defrost, it barely blows out the defroster vents and blows mosltly out the front dash vents. I located the vacuum switch by the tranny hump and it appears to be working. Must be another one up top somewhere?? Don't have a book on this truck. Any help would be appreciated. The truck is a 1987 bigblock with AC. Thanks, Greg

11-26-2003, 09:05 PM	#2
old Rusty C10 Robert Olson Transport Join Date: Oct 2002 Location: recent transplant to NC USA Posts: 20,277	check right behind the switches sometimes vaccum there screws up __________________ Bob 1951 International running on a squarebody chassis "If a man's worth is judged by the people he associates himself with, then i am the richest man in the world knowing some of the fine people of this board" http://67-72chevytrucks.com/vboard/a...t.php?f=25&a=9 (you can review the site rules here!) PM Me for your vehicle/parts hauling needs in the North East US or see my Facebook page Robert Olson Transport Live each day to the fullest.. you never know when fate is going to pull the rug out from under you... I hate cancer!!

11-27-2003, 03:06 PM	#3
Grim Reaper Registered User Join Date: Jul 2001 Location: Atlanta GA Posts: 1,704	The vacuum deal you found is for the floor vents. The one for the defrost is behind the box. Take the glove box door off. That will give you access to the top of the box. Might have to drop the ECM. What you will see is the Diverter control cable for the temp slide. Almost directly behind that is the vack pot for the difroster flap. You should be able to feel the vac line. Also make sure the Vac is connected under the hood. Factory the vac is connected to a "T" in front of the distributor. Yous should have a Vacuum ball, Check valve and then go into the truck. __________________ Grim-Reaper 70 Pontiac LeMans Sport Convertible, worlds longest resto in progress Looking for 71-72 2wd Blazer or Jimmy Project

11-28-2003, 04:29 AM	#4
Black872500 Registered User Join Date: Nov 2003 Posts: 7	Thanks, I'll give it a look. Greg



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