1997 Chevy Astro Front blower quits going up hill

RICKSTA

MEMBER
1997 CHEVROLET ASTRO
6 CYL
2WD
AUTOMATIC
183,000 MILES

When traveling on the highway (highway speeds) the font ac / heat blower shuts down while going up a hill. It then resumes back on when comming down the hill. It only does this going up hill on the highway and works fine going on level. It will not do it in town driving and will not do it going up hills in twn, Only on up hill grades on the hihway. When this happens everything else is fine. No loss of power no drop in the amp guage no headlight dimmimg, nothing. It does it with the cruise on or off. When it is working it blows strong. Again, only shuts down going up hill on the highway. Really got me stumped!

5 Replies

CARADIODOC

MECHANIC
33,871 POSTS

Hi ricksta. Welcome to the forum. Do you mean the fan turns off or the air starts blowing out of the wrong vents? Chrysler had a similar problem that didn't affect all cars but when it did, there was a simple fix.

This involves heater controls that are vacuum-operated. The load of going up a hill reduces manifold vacuum momentarily. When that happens, the heater controls are normally spring-loaded to default to the defrost position. It's a safety thing. Your feet might freeze but your windshield will be clear.

If you feel that air blowing onto the windshield when this happens, first look for a check valve in the vacuum hose between the engine and heater controls. In the case of the Chrysler vehicles, that valve rarely fails but there is a second version of it that includes a small vacuum storage canister. The original valve is about the size of two nickels. The replacement is about the diameter of a quarter and about 1 1/2" long. Replacement takes the better part of 15 seconds once the hood is open.

Caradiodoc

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Friday, June 25th, 2010 AT 12:27 PM

RICKSTA

MEMBER
3 POSTS

Hi, In reply to your answer to my question. No, the air from the blower (fan) does not does not change from the vents to defrost or such. This is why it has me stumped. I have done repairs myself to autos through the years with blower problems and the like and know about vacuum lines etc causing the air to redirect. But this is something I have never seen. There is no change. The only thing that happens is the fan turns off just as if you were turning it off and then turning it back on. ONLY going up hill and Only on the highway and highway speeds. Never in town or even going up hill in town and does it with the cruise on or off. Of corse I have checked connections in electrical, vacuum etc. I have pretty much always been pretty good at trouble shooting when it came to these kind of things but this one really is strange! I showed a friend of mine who is a mechanic for Chevy and he has never seen one do this. He says it must be haunted! Lol

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Friday, June 25th, 2010 AT 12:44 PM

CARADIODOC

MECHANIC
33,871 POSTS

Hmm. Is there a Body Computer involved? Or an HVAC computer with automatic temperature control? If not, I guess I would start right at the fan speed switch and monitor the voltage coming in to see if it drops out when the fan quits. Can you follow the circuit back to the previous point where you can take another voltage measurement? Say a fuse for example?

Caradiodoc

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Friday, June 25th, 2010 AT 1:28 PM

RICKSTA

MEMBER
3 POSTS

Well I gotta say I don't feel so bad about myself when it seems it even has you guys puzzled! It does not have a temp control or body temp controls. Just the old type of temp control. What makes it hard is all checks out good and works fine while parked or in town driving. Since it only does it going up hill on the highway at 50 to 70 mph it makes it hard to try to check. I wonder if some goofy strange thing in the vans computer would cause it but being it is the old temp control and basic fan switch type I would not think there would be any computer having anything to do with it. But I realize it always "old school" anymore with these systems. I think Im gonna run a temp hot line direct from the battery (fused) to the switch and try it. I can live with it but can you imagine driving in the highway and Every up hill grade it is just like you reach over and turn the fan off and then turn it back on as you go back down the hill.I just got back from driving to Florida from here in Missouri and it did it all the way down there and back. I recall going through Alabana and some of those long hill going up it would get prety warm in side as it would shut down but turned right back on as you came back down. What really gets me is I cannot get it to quit in town going up hills. I think I got one for the mystery book here! I relly want to thank you for your replys and if anything it is something to keep my brain working!

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Saturday, June 26th, 2010 AT 10:11 AM

CARADIODOC

MECHANIC
33,871 POSTS

What you should do is connect a clip lead directly to the fan switch, then connect the other end to a test light or voltmeter that you can monitor while you're driving on the highway. When the fan quits, if the test light stays on, the problem is after the switch or in the motor's ground wire. If the light goes out, there's an intermittent break or connection before the switch. Move the clip lead around to different points in the circuit to find the break.

Caradiodoc