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HVAC slows/turns off on hills.
#775843 May 09th 2021 9:12 pm
Joined: Sep 2015
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1987 G20
When climbing hills, the HVAC will slow eventually turning off depending on how steep the hill is. Once the road levels out, HVAC will blow again.
I read vacuum check valve??
Getting ready for the summer road trip so I think it's time to finally fix the issue.
Thanks.

Re: HVAC slows/turns off on hills.
chevydude1987 #775847 May 09th 2021 10:01 pm
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Chevy motors will go into self preservation ...

when the load on the motor get to be too much it will shut down the air 1st.

its a natural thing no fixin required. even if you get a bigger motor then it will still do it even my 454 does it.


SUNSHINE VANS-VAN DIEGO
ADRENALIN BY THE GALLON & CHASIN RACIN
ONE FOR THE DIRT & ONE FOR THE STREETS
'93 CHEVY G30 454 4X4 SPORTVAN EXT 146" WB
'92 CHEVY G30 454 BEAUVILLE EXT 146" WB
Re: HVAC slows/turns off on hills.
chevydude1987 #775854 May 09th 2021 10:58 pm
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Good to know that's normal, but kinda sucks, but no biggie.
Oh ya, I have got to go back to the salvage yard out in san Diego.

Re: HVAC slows/turns off on hills.
chevydude1987 #775858 May 09th 2021 11:49 pm
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My 2000 Astro with 4.3 L6 does the same. Though I will say my Astro has a "normal" and "maximum" A/C setting. On the normal mode I hardly notice, but on really hot days I'll kick on max for a while, and if I'm driving around the very hill heavy city of Staunton where we used to live I notice it a lot more on the max setting, and even more so if she kicks into passing gear.


[Linked Image from live.staticflickr.com]

Re: HVAC slows/turns off on hills.
chevydude1987 #776156 May 15th 2021 6:59 pm
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you have a vacuum leak somewhere. there should be a round bulb under the hood thats a vacuum reservoir, might be bad or have a leak in the line.

1 member likes this: NateB
Re: HVAC slows/turns off on hills.
V30crewcab #776262 May 17th 2021 8:55 am
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Originally Posted by V30crewcab
you have a vacuum leak somewhere. there should be a round bulb under the hood thats a vacuum reservoir, might be bad or have a leak in the line.


I second that!


Nate Breece
--------------
1993 Chevy G20
2012 Hyundai Santa Fe
Re: HVAC slows/turns off on hills.
NateB #776297 May 17th 2021 6:29 pm
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Originally Posted by NateB
Originally Posted by V30crewcab
you have a vacuum leak somewhere. there should be a round bulb under the hood thats a vacuum reservoir, might be bad or have a leak in the line.


I second that!

I third that....
Vacuum leak somewhere in the control tubing for the heat/AC or a bad check valve or a bad reservoir. Manifold vacuum drops when the engine is pulling causing the system to go into heat, shifting the blower output to the floor vents or to defrost. Check the vacuum line to the hot water valve on the heater hose first as they are bad to just come loose or be broken. The vacuum hose to the reservoir is prone to stress as well from opening and closing the hood.

Happy hunting....

Last edited by CatFish; May 17th 2021 6:37 pm.
Re: HVAC slows/turns off on hills.
chevydude1987 #778977 July 15th 2021 9:25 pm
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I retract my previous statement thinking it was normal, and add me to the vacuum leak crew now. Here's why, hope this helps.

So Mine had done it since I got it, must have had a crack in the hard line that goes from the intake to the little junction behind the A/C accumulator, as those harder vacuum lines are often brittle and crack.

I recently had the local Chevy dealer do an intake gasket on the Astro, and they screwed up a whole boat load of stuff, but one of the things I found was my upper dash vents weren't blowing out much air at all. When I popped the hood I immediately found this open vacuum barb and a bunch of missing hose that the tech forgot to put back.

[Linked Image from live.staticflickr.com]

This is right behind the A/C accumulator and it actually goes from there to a little T fitting which has the super tiny hard hose going to the intake (blue line in the attached image) and also has normal rubber hose going off to the Vacuum Reservoir (red line in the attached image). All of that was missing on mine, but I bet your issue is just in the blue line being cracked.

[Linked Image from live.staticflickr.com]

I went to pull all this at the junkyard today and the hard line on the donor vehicle broke as well, so what I did was just use a few feet of rubber line that fit snuggle over the outside of the tiny hard line. At each end I left about an inch of hard line sticking out of the rubber 90 degree boots, then just slid the rubber line over each and routed it above my intake hose.

My A/C is blowing cold and powerful now and doesn't slow down when under a load. Hope this helps you get your issue sorted. Let me know if you need any more pictures or info.


[Linked Image from live.staticflickr.com]


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