Defrost Setting

[Greg C.]

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
Knoxville, TN

"Ruby Sue"
1977 Royale
Rear Bath
403 Engine
American Eagle Wheels
Early Version Alex Sirum Quad bags

 

[T McManus]

Greg
I also have a 77 Royal rear bath. I had the same problem you are having. I put some pictures of the Air box on
http://www.gmcmhphotos.com/photos/g7332-1977-hvac.html for reference. I sent you a PM.
--
Tom McManus
1977 Royale

Chesapeake VA

 

[john r. lebetski]

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

 

[JShot]

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