AC/Heater problems... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

r0lf- · 11-03-2003, 05:25 PM

Well... I just installed a new blower motor in my truck in the last week or so. It works great and all, my heater blows really warm and my AC needs a recharge (what a suprise).

I have a bit of a dilema though, this interior has been updated to the new 87 interior, not the stock 78. Sooooo... the issue is, that when I goto place the controls for the heater on the defrost vents for the windshield, the vents arent opening, but the AC motor turns on. This is somewhat confusing me.

I remember on another post someone said that the vents are vaccum controlled, but I dont know where to look to enable this... so If anybody could post some shots or shoot me some info, id appreciate it.

soleeagle · 11-04-2003, 12:00 AM

I recently had the same problem in my 85. I ended up tearing most of the underside of the dash apart and could find nothing. I know that the switch was vaccume controlled but couldnt find anything wrong. I then found 1 vacume line running out threw the firewall. I trced it under the hood and found that it was just wire tied to the firewall and didnt go any where. I hooked it up to the vaccume port on the motor and it works great now. It was aparently unhooked when the previous owner took out the 305 and put in the 350. I didnt know I needed it when I rebuilt my motor and overlooked it when I put it in. Hope this might help you. The hose came out on the passenger side of my truck.

crackajacka · 11-04-2003, 03:37 AM

could this also not make the blower motor work? my system is dead it did work at one time lol

soleeagle · 11-04-2003, 11:36 PM

My blower motor would work fine. The air would only come out on the floor and would not change untill I hooked up the vaccume line.

77 Shortbed · 11-08-2003, 12:49 AM

There should be a reservoir on the passenger side of the firewall. It's black and is kind of round or oval in shape. It usually draws vacuum from the intake. Make sure you have vacuum there first.

The line from the reservoir then runs to the back of the heater control switch in the dash. There is a diaphram valve under the dash behind and sightly to the left of the glove box that operates the "door" the changes the air flow from the floor to the vents, to the defroster. Once you make sure you have vacuum at the reservoir you should be able to hear the diaphram move the "door" from one position to another. That is when everything is connected correctly.

r0lf- · 11-09-2003, 05:17 PM

thats what it was. It just wasnt hooked up.

soleeagle · 11-10-2003, 01:02 AM

Isnt it so cool when you think you have a major problem and it ends up being something so simple?

KShortell · 11-10-2003, 12:12 PM

Glad ya found it!

BillG_69gmc · 11-10-2003, 10:59 PM

I am currently working on getting my heat & a/c controls working again. Now I'm ok with getting the vacuum into the cab... and I believe the main vacuum line gets hooked up to valve #1 (my control unit has numbered stems) now the remaining two stems.... I'm not 100% on.

Does someone have a simple flowchart of what vacuum lines hook to what.

I know that one line T's off and shares the line for vacuum controller under the glove box.

There is also a control just the other side of the firewall...passenger side also.

Any info or link to a drawing would be nice.

And finally the vacuum control hot water valve. Which leads to my final question...The valve is not labeled for direction, and frankly I don't know what direction the water would be flowing, BUT since the valve is a plunger type, it seems that I would want to know for sure that it goes one way or another or does it matter? I just would not want hot water forcing its way thru when the a/c is on, if that were the case.

Thanks Guys n Gals

billg
69 gmc

11-04-2003, 12:00 AM	#2
soleeagle Registered User Join Date: Sep 2003 Location: Shelbyville, Indiana Posts: 614	I recently had the same problem in my 85. I ended up tearing most of the underside of the dash apart and could find nothing. I know that the switch was vaccume controlled but couldnt find anything wrong. I then found 1 vacume line running out threw the firewall. I trced it under the hood and found that it was just wire tied to the firewall and didnt go any where. I hooked it up to the vaccume port on the motor and it works great now. It was aparently unhooked when the previous owner took out the 305 and put in the 350. I didnt know I needed it when I rebuilt my motor and overlooked it when I put it in. Hope this might help you. The hose came out on the passenger side of my truck. __________________ Chuck '85 Chevy Silverado 4X4 '91 Chevy 4X4 Suburban http://www.cardomain.com/memberpage/545941

11-04-2003, 03:37 AM	#3
crackajacka Stylin Join Date: Sep 2001 Location: Tuttle, OK Posts: 620	could this also not make the blower motor work? my system is dead it did work at one time lol __________________ Ive been traveling for some time, with my fishin pole and my bottle of shyne. Most Girls like finished products and just dont understand what a good addiction does for you http://www.paulwall.us/

11-04-2003, 11:36 PM	#4
soleeagle Registered User Join Date: Sep 2003 Location: Shelbyville, Indiana Posts: 614	My blower motor would work fine. The air would only come out on the floor and would not change untill I hooked up the vaccume line. __________________ Chuck '85 Chevy Silverado 4X4 '91 Chevy 4X4 Suburban http://www.cardomain.com/memberpage/545941

11-08-2003, 12:49 AM	#5
77 Shortbed Registered User Join Date: May 2003 Location: Central Indiana Posts: 16	There should be a reservoir on the passenger side of the firewall. It's black and is kind of round or oval in shape. It usually draws vacuum from the intake. Make sure you have vacuum there first. The line from the reservoir then runs to the back of the heater control switch in the dash. There is a diaphram valve under the dash behind and sightly to the left of the glove box that operates the "door" the changes the air flow from the floor to the vents, to the defroster. Once you make sure you have vacuum at the reservoir you should be able to hear the diaphram move the "door" from one position to another. That is when everything is connected correctly. __________________ 77 Shortbed, 4x4, 454, sm465/205, 33x12.5x16.5.

11-09-2003, 05:17 PM	#6
r0lf- Hotwheels? Join Date: Dec 2002 Location: Pleasant Hill, CA Posts: 1,145	thats what it was. It just wasnt hooked up. __________________ 1978 Money Pit - CUSTOM DELUXE!!!!

11-03-2003, 05:25 PM	#1
r0lf- Hotwheels? Join Date: Dec 2002 Location: Pleasant Hill, CA Posts: 1,145	AC/Heater problems... Well... I just installed a new blower motor in my truck in the last week or so. It works great and all, my heater blows really warm and my AC needs a recharge (what a suprise). I have a bit of a dilema though, this interior has been updated to the new 87 interior, not the stock 78. Sooooo... the issue is, that when I goto place the controls for the heater on the defrost vents for the windshield, the vents arent opening, but the AC motor turns on. This is somewhat confusing me. I remember on another post someone said that the vents are vaccum controlled, but I dont know where to look to enable this... so If anybody could post some shots or shoot me some info, id appreciate it. __________________ 1978 Money Pit - CUSTOM DELUXE!!!!

11-10-2003, 01:02 AM	#7
soleeagle Registered User Join Date: Sep 2003 Location: Shelbyville, Indiana Posts: 614	Isnt it so cool when you think you have a major problem and it ends up being something so simple? __________________ Chuck '85 Chevy Silverado 4X4 '91 Chevy 4X4 Suburban http://www.cardomain.com/memberpage/545941

11-10-2003, 12:12 PM	#8
KShortell Registered User Join Date: Oct 2003 Location: Chesapeake, VA Posts: 734	Glad ya found it! __________________ Semper Paratus

11-10-2003, 10:59 PM	#9
BillG_69gmc Registered User Join Date: Feb 2003 Location: Georgia Posts: 9	vacuum lines heat & a/c I am currently working on getting my heat & a/c controls working again. Now I'm ok with getting the vacuum into the cab... and I believe the main vacuum line gets hooked up to valve #1 (my control unit has numbered stems) now the remaining two stems.... I'm not 100% on. Does someone have a simple flowchart of what vacuum lines hook to what. I know that one line T's off and shares the line for vacuum controller under the glove box. There is also a control just the other side of the firewall...passenger side also. Any info or link to a drawing would be nice. And finally the vacuum control hot water valve. Which leads to my final question...The valve is not labeled for direction, and frankly I don't know what direction the water would be flowing, BUT since the valve is a plunger type, it seems that I would want to know for sure that it goes one way or another or does it matter? I just would not want hot water forcing its way thru when the a/c is on, if that were the case. Thanks Guys n Gals billg 69 gmc



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