Dash A/C Cycles on and off during acceleration

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czlight

Member
Joined
Aug 8, 2006
Posts
9
Location
Near Kennedy Space Center
Hi,

I just purchased a 1993 Coachmen 340mb limited. During the test drive the previous owner pointed out that the dash a/c will sometimes cycle off for a few seconds during acceleration then back on after the engine levels. Has anyone ever heard of this before?

Thanks in advance for your help.

Chuck
 

John From Detroit

Well-known member
Joined
Apr 12, 2005
Posts
25,114
Location
Davison Michigan
Well, I have the same problem with my towed car, it was real bad a while ago but I got it repaired so it's now back to normal

And what you describe is NORMAL

Story: While I had my RV back at the factory for some warranty work I had a nice chat with the AC technician there, Now understand since we were talking about my 1992 Lumina APV and not the 2005 RV there was no reason for him to tell me anything untrue.

Understand further I confirmed what he told me with some service manuals

A/C draws a lot of power, in the old days (Back when we had big engines and breaker point iginations) there was power to spare so we more or less forgot it, but with today's newer, smaller, more fuel efficent engines there is not as much spare power, to the AC is actually run not by the dash switch, but by the car's computer system.

And when you call for heavy duty acceleration, in order to get the most power to the wheels, it cuts off the AC.  This is for cars, Motor homes the AC is a much smaller (percentage wise) portion of the load on the engine, however since the technology  is there, they use the same type of computer and programming/  So what you describe is Working As Designed.

Your 1993 likely also uses vaccume to decide when full accelaration is called for.

I had other clues (Poor cruise control operatoin) that there may be a vaccume problem and sure enough there was, Bad servo on the Cruise (Valves leaking) Dealer replaced and though the AC still cuts out if I floor it,,, It hangs in there if I'm gentle on the pedal

You might wish to check all vaccume hoses and devices.. Since it's a teenager, it's time to do that anyway

Now... one thing that can make a difference.  As I said, my car it got real bad.  We investigated and found a vaccume leak (On my car the computer decides I want full acceleration by measuring vaccume, My motor home is a bit different in that regard)

 

Shayne

Well-known member
Joined
Jan 22, 2006
Posts
4,324
czlight 
That's characteristic of the 93 Coachman Special MB340  Ours did the same thing for 72000 miles and probably still doing so.  In hilly terrain when it took lots of vaccuum we would turn on the generator and run the house air so as to eliminate the use of the dash air and free up the vac needed for driving.. 
 
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