| Defrost Setting [message #359556] |
Sun, 18 October 2020 11:38  |
Greg C.
Messages: 224
Registered: October 2019
Location: Knoxville, TN
Karma: 0
|
Senior Member |
|
|
I have read on this forum and in the manual about the HVAC system on my coach.
One thing I came across more than once is that it should FAIL in warm/defrost mode.
Well, mine will not defrost. It seems like I also read that defrost mode is zero vacuum, or vacuum bleed position. I only have air coming out of the AC vents, hardly any at the heater vent, and none at the defrost vent, no matter what position the control is in. The vacuum line plug is tight on the back of the control.
Is there any position on the control where the main vacuum source line would hold vacuum?
Any suggestions on the Defrost issue?
Greg Crawford
KM4ZCR
Knoxville, TN
"Ruby Sue"
1977 Royale
Rear Bath
403 Engine
American Eagle Wheels
Early Version Alex Sirum Quad bags
|
|
|
|
|
|
| Re: Defrost Setting [message #359683 is a reply to message #359556] |
Wed, 21 October 2020 17:51  |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
|
Senior Member |
|
|
Yes. No vacuum defaults to DEF on GM (Mopar too I never worked on Ford). Perhaps PO did something or something fell down the defrost duct. Disconnect and plug the vacuum source at the engine manifold as a test. If you get DEF air then vac motors and doors are probably good and look at the dash control. If no change look at vac motors and doors.
John Lebetski
Woodstock, IL
77 Eleganza II
|
|
|
|
| Re: Defrost Setting [message #359770 is a reply to message #359556] |
Sun, 25 October 2020 15:20 |
 |
JShot
Messages: 485
Registered: October 2006
Location: NW Ohio
Karma: 0
|
Senior Member |
|
|
Greg, don't know if this has anything to do with your 'no defrost air' problem, but here's what we found on our '78.
As you know, the later coaches had the two, large defroster vents in the dash (as opposed to all of those many smaller ones on early coaches.
The two long edges of each of the two vents (are supposed to) have a "long U shaped" metal cover on them, I'm assuming for two reasons.
1) to hide the unsightly edge of the plastic vent, and 2) to keep the edge from forming itself into a fancy curve.
During the "destruction" of the dash along with our total gut and rebuild of the coach, that defroster assembly was removed from its normal position, and guess
what we found inside - the metal strips. Amazing how much air blows out onto the windshield now.
HTH,
John
John Shotwell
Ridgeville Corners, OH
78 Royale Center Kitchen
|
|
|
|
GMCforum
Search
Help
Register
Login
Home
