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Only blows when moving

antne on Sun August 21, 2011 7:14 PM User is offline

Year: 1995
Make: Chevy
Model: Blazer-s10
Engine Size: 4.3
Country of Origin: United States

I have tried everything for the past month to figure out why my A/C only blows when the car is moving. I have a new blower motor, blower switch, blower relay, checked vacuum hoses. But I cant figure it out. Everything else works and when it blows it is nice and cold. I stop the car at a stop sign or at a stop light and the air stops blowing until I get moving again. Any suggestions? compressor and its connection is new, accumulator and connection is new, hose is new, connection into relay is new blower motor is new, blower switch is new and vacuum switch is new everything purchased within this summer and has been working fine until the past month.

mk378 on Sun August 21, 2011 7:28 PM User is offline

The blower motor does not run? The ones without electronic control panel have a couple of relays and a resistor in addition to the motor, switch and fuse.

antne on Sun August 21, 2011 7:46 PM User is offline

the blower motor seems to only run when the car is moving - because that is the only time the air is blowing out of the vents. I have all new relays, fuse is good, new motor havent tried resistor because I understood that the resistor controls lower speeds of the blower and it works on the lower speeds, but just doesnt blow air until the car is in motion

mk378 on Sun August 21, 2011 8:00 PM User is offline

Some air will come out even without the blower because it gets rammed into the intake duct when the truck is moving. You could unplug the motor to see if it really is a case of the motor starting and stopping, which would be very unusual. If it acts the same with the motor disconnected, the motor is never starting.

Or just pull a diagram of the car and troubleshoot the blower circuit. Generally the first place to start is to measure the voltage between the motor terminals to see if it is getting any power. If there is battery voltage but it doesn't run, bad motor.

Edited: Sun August 21, 2011 at 8:01 PM by mk378

GM Tech on Sun August 21, 2011 8:10 PM User is offline

The normal complaint is, it doesn't blow cool air while stopped--- Is air blowing, just not cool? I can't even imagine your blower motor shutting off at each stop light. More likely the a/c compressor is shutting off at each stop. If so you probably are experienceing high pressure cut-outs of your compressor- and need more air flow across your condenser while stopped-- as in your fan clutch is inop- and you need to replace it.

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

antne on Sun August 21, 2011 8:28 PM User is offline

I will try disconnecting and see if it works the same or not. But I almost positive that it is as it was just replaced and I made sure it worked before hooking it up. There also is a definite difference between blowing air or air just blowing in because it is cold air as it is when running normally. I will try disconnecting and post the results shortly. Thanks

antne on Sun August 21, 2011 8:40 PM User is offline

GM Tech - no, there is no air blowing at all. Cold or Hot. It just stops until I start moving again. As to the compressor, it does not seem to cut off (I am very familiar with the sound of the compressor-I have had issues with that not too long ago due to short in connection-compressor is new as well as connection now) Now as to the air flow across the condenser, if it were the clutch fan, wouldn't there also be issues with overheating as well? I have changed clutch fan few years ago and I recall having major issues with overheating which caused me to replace it. Also whether the compressor was running or not it would not effect the blowing of the air from the vents, correct? Only the issue of the air being hot or cold? If so, then that is not the case as the air, when it blows is cold. Please advise me on my clutch fan questions, so I can rule it out or keep it in consideration. I will wait your response. Thanks for your help

GM Tech on Sun August 21, 2011 9:00 PM User is offline

Bad fan clutches always show up first with a/c concerns, not engine overheating concerns.

You say it stops blowing, I doubt that- I would say that the air flow is being directed somewhere else, like out the defrost-- but usually the complaint is just the opposite, the air "quits" while accelerating, and blows out vents at stops.....

In my 30 years, I have never heard of a blower motor that stopped working only when vehicle stops.

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Dougflas on Sun August 21, 2011 9:05 PM User is offline

Not sure on your electrical ability to troubleshoot so forgive me if this sounds "insulting". You need to verify 12volts is reaching the motor. Place a 12 volt lamp from the motor hot terminal and motor ground. Run the lamp wires into the vehicle while you drive and stop. The light must stay on. If not, get back to us and we can give step by step troubleshooting. Do you have a schematic of the AC system?

antne on Mon August 22, 2011 7:09 AM User is offline

Okay, unplugged motor and yes, it was the same. So took motor out - exchanged it - put new one in and nothing different. I used a voltage tester and there is power going to the motor. The wires that go to the relay, the ones that should have power going through them do. Same with the resistor. Now I couldn't have got another bad motor could I? Although when I put the previous one in I do recall it blowing harder initially, so maybe because it was working.

When I went to switch it out, the guy at the store said maybe there was a voltage problem. Suggesting something is frying the motor. Wouldn't it fry the relay or resistor first? or wouldn't it at least work for a bit like the last one? I mean it wouldn't be the first time I have had to take a part back more than once because I was given a defective one. How about the controls? someone suggested the a/c switch may be bad. But that wouldn't have anything to do with making the motor run, would it?

Let me know what you think. Im up to try anything. I have spent to much money and time fixing to get in good running condition. But without the a/c, all the money and work I recently put in feels like waisted time and effort. Would rather have a/c and have the truck run like $#!+. lol thanks

mk378 on Mon August 22, 2011 7:25 AM User is offline

With everything plugged in, turn key on, set switch on high, measure the voltage between the two terminals on the motor. In other words push one probe into the back of one pin on the motor plug and the other one into the other pin.

Examine all connectors for evidence of overheating or melting.

Edited: Mon August 22, 2011 at 7:26 AM by mk378

tvlunn on Mon August 22, 2011 11:26 AM User is offline

I have a couple of ideas ................. but I first need to know a couple of things:

1- While the auto is in motion, do you have the ability to switch fan speeds (low, medium & high) and the fan respond appropriately?
2- When the auto comes to a stop, does the fan always maintain the same speed as while the auto was in motion?

mk378 on Mon August 22, 2011 12:54 PM User is offline

Really, it doesn't matter about moving or not. Get it to run like it's supposed to when the truck is stopped.

tvlunn on Mon August 22, 2011 3:20 PM User is offline

Well, that was my intention! However, I do need some information to help understand what he may or may not be experiencing .............. I'm not there to "see" for myself and therefore can't really be sure what is occurring. So, I was simply asking questions in order to help diagnose or troubleshoot the issue. How else can one help get it running correctly without information.

My approach to some issues may not seem so obvious .................. I do hope you can help the gentleman

jglanham on Tue August 23, 2011 6:47 PM User is offline

The process of elimination is the key to solving any issue.
You indicated that the blower works on lower speeds. This indicates that the blower motor runs. On many vehicles, the blower fan will run when the ignition key is on, without the engine running. (much easier to hear blower without engine noise).
Have you tried operating the heater instead of the a/c? Did the blower work normally or have the same issue? Do all speeds work? If it has the same issue, try starting the engine and rev it in neutral or park. Does air start flowing? (possible vacuum actuator issues) If your vehicle uses vacuum operated actuators, you could have a leaky actuator. Have you checked vacuum lines to see if one has fallen off or was removed or inadvertently connected wrong when working on the a/c system? If it has electric actuators, have you checked the connectors?
If the above doesn't solve the issue:
Hook-up a voltmeter as suggested by mk378. Measure the voltage with the fan switch on high. It should be 12 volts or more and should be present when on Heat or A/C, whether or not the vehicle is moving.
You also did not mention if you had an ATC system (Automatic Temperature Control). If you do, and the above information did not help to solve the issue, you could have a faulty control module.
Another long shot possibility is that if you rev the engine and the blower starts working, and there were no actuator issues, the increased voltage from the alternator is boosting the voltage on a faulty connection or module enough to make it work.


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