The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1973 - 1987 Chevrolet & GMC Squarebody Pickups Message Board

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 02-07-2003, 01:15 PM   #1
Marks 85
Color By Krylon
 
Marks 85's Avatar
 
Join Date: Jan 2003
Location: Benbrook Tx.
Posts: 179
Heater Defrost

When I switch the knob to defrost it dosent blow out of the top of the dash. Are these controlled by vacuum or manual?
Marks 85 is offline   Reply With Quote
Old 02-07-2003, 01:47 PM   #2
Blue Beard
Registered User
 
Blue Beard's Avatar
 
Join Date: Jan 2003
Location: Washington State
Posts: 8,831
I've got a similar problem, also have a/c and was told that the diverter box is probably to blame.....
__________________
1970 Chev CST
2003 Harley Fatboy
1975 Chevrolet Step Van
1956 Chev Bel Air
1977 Blazer 2WD For Sale $3000.00
1978 Blazer 2WD For Sale $7000.00
1978 Silverado
2005 Monte Carlo
Blue Beard is offline   Reply With Quote
Old 02-07-2003, 02:34 PM   #3
bigd65
Registered User
 
bigd65's Avatar
 
Join Date: Mar 2000
Location: Clute, TX.
Posts: 1,935
check the vacuum ball under the hood. that is the reserve vacuum that controls the heater controls. if not could be the control panel itsself on you dash cluster
__________________
2004 Silverado Crewcab
1972 Chevy Monte Carlo
2017 Chevy Tahoe
bigd65 is offline   Reply With Quote
Old 02-07-2003, 02:38 PM   #4
PHOENIX
Registered User
 
Join Date: Oct 2002
Location: Phoenix, Arizona
Posts: 4,703
I only have expierence with Heat Only Controls:
The defrost should be controller mechanically. There is a little cable that hooks to the control panel, the cable then opens up a little "door" to allow the heat to change directions. Check the cable at the control panel, then follow it. Check to see if the "door" opens ans closes, your should be able to hear it.

There is not much that can really go wrong with the heat only models.

Is your blower fan working? Without that fan on you will only get circulation when moving, and it isnt very much.
__________________
* AVOID: LOPER'S PERMORANCE / LOPERSPEED.COM OF PHOENIX, AZ & COTTMAN TRANSMISSION *
PHOENIX is offline   Reply With Quote
Old 02-08-2003, 03:02 AM   #5
apstguy
LED King
 
apstguy's Avatar
 
Join Date: Jan 2003
Location: Sacramento, CA
Posts: 2,087
I just tore apart my ventilation system in mine so I have some experience with it.

On A/C models, it is controlled by vaccuum. One or two of these could have caused a no defrost problem. To check and see if it is the door to the defroster itself, take the floor outlet cover off (one screw - not too hard). With your truck running, turn it to defrost, if the door closes to the floor vent, that vaccuum motor is good. If it didn't close, you need to follor the vacuum line from it to the control panel and try to find a leak.

Your main air diverter might be dead also.

Use process of elimination to figure this out. Does it switch between floor to vents? If it does not, your main air diverter might be dead.
__________________
Tyler

1985 C10 305 w/ Bowtie OD TH700R4 3.42 LSD 202,000 miles
2006 Ford Focus ZX3 5-speed Stick
2016 Chevy Spark EV
Gone: 2002.5 VW GTI 24v VR6
Gone: 2008 VW R32
apstguy is offline   Reply With Quote
Reply

Bookmarks


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 09:04 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com