Use of A/C causes soft brake pedal

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  #1  
Old 10-14-04, 02:20 PM
Rusty Maxwell
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Use of A/C causes soft brake pedal

1991 Honda Accord...Use of the air conditioner causes the brake pedal to become very soft. Depress the pedal and it will reach the floor in about 3 seconds. If the A/C is not used, then brake action is completely normal..very solid. Thus, this problem reoccurs every summer and goes away in the Fall and Winter. Someone mentioned I might have a vacuum problem somewhere. I'll take suggestions on where to start looking.
 
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  #2  
Old 10-17-04, 02:15 PM
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Where are you located I would like to see this in person or have someone I know evaluate it.
 
  #3  
Old 10-18-04, 05:16 AM
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dose tne rpm fall off iwhen the ac is on yes you can have a vaccume leak but you may also have a low vaccume problem in the fiest place get a vaccume gage and check your manifold vaccume with and without the ac on you have to start there
 
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Old 10-18-04, 09:58 AM
Rusty Maxwell
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Originally Posted by davo
Where are you located I would like to see this in person or have someone I know evaluate it.

I am in Iowa City, IA.
 
  #5  
Old 10-18-04, 02:18 PM
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This is very strange. WOuldn't a low vaccum problem cause a very stiff pedal, not a very low pedal?
 
  #6  
Old 10-18-04, 04:16 PM
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For the life of me, I can't see any connection there. The only remote idea might be the A/C dishcarge line being too close to a brake line and boiling the fluid. Other than that, it makes no sense.
 
  #7  
Old 10-18-04, 04:34 PM
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Some cars used engine vacuum..

to operate the doors and mode selections, but I don't see how the controls could bleed enough vacuum to effect the brake booster. The A/C does put more of a load on the engine and maybe the drop in RPM is enough to cause low vacuum. I think some year hondas use a special wire from the alternator to sense engine load and adjust the RPM.

I would check manifold vacuum with the A/C on and off. I would also look closely for any cracked hoses or other vacuum leaks.

Just some random ideas, hope this helps.
 
  #8  
Old 10-18-04, 04:40 PM
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however, what the poster describes sounds more like a situation when your m/c goes out, or you have no fluid. a loss of vaccum's gonna cause the pedal to get very stiff, and no go down at all, quite the opposite problem he is describing.

What he describes sound like a brake bleeding issue, or a bad m/c. Perhaps it is a mere coincidence between the relationship.
 
  #9  
Old 10-19-04, 04:11 AM
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Originally Posted by Desi501
For the life of me, I can't see any connection there. The only remote idea might be the A/C dishcarge line being too close to a brake line and boiling the fluid. Other than that, it makes no sense.
Thank you that's the point I was trying to make.It does not make sense at all.
 
  #10  
Old 05-22-06, 09:35 AM
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I have the same issue with my 1992 Accord wagon.. I just replaced the brake pads, shoes, wheel cylinders and the system flushed.

I have noticed that this will also happen when the car is in stop and go traffic more than anything else.

I had several issues with the Break-O (intentional) that did the work as they crossthreaded 8 lugnuts (causing 2 posts to break and 4 lugs were badly damaged and were replaced).

I may have to do a good system flush and then swap the master cylinder. I hope it isn't the booster as it is not cheap.
 

Last edited by paarlberg; 05-22-06 at 04:51 PM.
  #11  
Old 05-22-06, 01:27 PM
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could it be because the engine boosts the engine rpm to compensate for the a/c load???
 
  #12  
Old 05-22-06, 04:50 PM
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Mine will even do it without the air on.. If in stop and go traffic for 10-15 minutes it will start feeling very soft.. and it will stay that way. I did notice that there is some corosion on the booster at the master cylinder level and below. However, it is dry and the fluids are topped up. I am assuming this was caused by an earlier bad master cylinder or someone trying to fill the brake fluid with their eyes closed.
 
  #13  
Old 05-23-06, 11:57 PM
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Think you have air in lines or soft seals in brake system that hardens in the cold.
 
  #14  
Old 05-24-06, 05:59 AM
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I agree.. I guess I have a project for the weekend now
 
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