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peterpete190, Auto Technician
Category: RV
Satisfied Customers: 27051
Experience:  Over 17 years diagnosing and repairing various model vehicles.
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I have a '93 Chevy G30 cutaway van RV and the HVAC system doesn&#

Customer Question

I have a '93 Chevy G30 cutaway van RV and the HVAC system doesn't obey inputs from the dash control. I saw the 5 yr old post to U re mode and blend doors that said "incorreect response to command resulting in incorrect direction of airflow and realized you're familiar w the problem.
Here's what mine is doing: If you're not moving and set it on "norm A/C" it comes out the dash vents OK but when U get up to freeway speed it will switch over by itself to push air out the floor and dash vents but sometimes it will also switch back to dash by itself (intermittently) But also on that big vent flap on the outside of the R footwell, the door will close when U put it to "max" which I think it should and then open in all other positions, but this allows freezing air to come in from outside blasting your feet when the control is set for heat in cold weather. So I want it to stay coming out dash vents on norm A/C and I want that vent to close on the R footwell when the heat's on. Can U make sense of this? Also I should say I can't help but suspect that when the guy replaced the heater core and had the dash partly out(bungied up) he may have knocked or misrouted something in there. Thx Gus
Submitted: 1 year ago.
Category: RV
Expert:  peterpete190 replied 1 year ago.
My name is ***** ***** I am a professional here at Just Answer. I noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.
From what you have described here this sounds like a loss of vacuum to the heater controls as the doors are controlled by vacuum.
I suspect a loose or damaged vacuum line under the dash or on the engine leading into the dash causing this here needing repaired,connected properly or replaced.This will need checked into further to pinpoint and repair the cause here.
Thanks Pete
Customer: replied 1 year ago.

pete; You'll have to bear with me on this one cause I don't know how long it's going to take me to test the lines in the system. I thought you're supposed to hook up a vacuum gauge to the system maybe at the big vac pot under the hood and see if it bleeds down or hold vacuum(?) Thx Gus

Expert:  peterpete190 replied 1 year ago.
I would listen for any vacuum hissing in the dash area or engine area with the engine running as this will help locate the fault.
Thanks Pete
Customer: replied 1 year ago.

Pete; A couple things: I should have said I'm a 40yr bodyman w a lot of mechanical repair mixed in and do stuff like fault tracing electrical, HVAC etc over the yrs, but this particular prob is odd as 1) It's intermittent, and doing the mode changes on it's own accord w/o any inputs(see my original description of the problem) and 2 I doubt V much if I'm going to hear any little vac leak hiss w a 350 V8 right there rumbling a foot from the dash. Also U didn't mention the old trick of spraying starter fluid around which I thought everyone used to find vac leaks watching for revs to go up. and I'm wondering why U didn't comment on the idea of doing a vacuum leakdown test. Last I'd like an answer to how familiar U are w the G30 cutaway van specifically and it's various complications with line routing, mode doors and blend doors which show a history of going bad after this much time. I don't mean to offend or diss U but I'd prefer to work w someone who has actually worked under the dash of a G30 van. (Have you???) I'm a real up front kind of guy and when I have Qs for a mechanic I won't be afraid to ask them. I'm going to send you the link to the reply one of the guys gave a customer w this same problem as food for thought also. And please don't hesitate to consult w one of your peers on Justanswer as I've know you guys to do in past Qs I've asked. But first I'll spray some starter fluid around and keep the ear open for anything unusual. If the fault is indeed under the dash it's going to be a bi$#* to find. I fear the dash may come out but not until last resort. Let know if this link comes thru:

Expert:  peterpete190 replied 1 year ago.
I have some experience with this model but not a whole lot.It is best for me to open your question up for others here to see if anyone else can assist further on this that may have more experience.I hope you can get this resolves with ease.
Thanks Pete
Customer: replied 1 year ago.

Pete; Appreciate your honesty. My BS detector works V well after 40yrs of dealing w tecs. In yrs of consulting w guys on this site I've come to expect this where if a guy wasn't sure he would check w other tecs. Meanwhile I got a factory shop manual on fleabay (came today) and it's incredibly detailed on the HVAC system showing ALL vac pots controls, lines, wiring, ductwork etc etc which should help me find places to look for trouble. BTW the tec I mentioned in that link is Ivan an ASE master tec and instructor. Hopefully we'll have a guy chime in whose had his nose into this dash before over HVAC trouble and work this out committee fashion HA. I'll make it a point to go out tomorrow and do some starter fluid spraying. Should have said before we replaced the old line from the big vac tank under the hood and that's about the only damline there is that ain't buried under the dash. Last and I think it may come to getting into the dash mess, I may just decide to leave the damthing alone cause it will still cool the cab even when it does it's self switch to come out the defrost and floor vents and not the dash vents. We actually crossed Death Valley last spring and more of the hot SW w it going goofus like that so it's not like I have no A/C at all. I'll stay w our attempts at diagnosis for awhile though. Thx again for your candor, Gus