Bus compressor will not build pressure between 60 & 90 lbs

by Buzz
(Okeechobee Fl USA)

I have an MC9 bus that will only build pressure between 60 & 90 lbs by racing the engine. After it reaches 90 lbs it works as good as it ever did. The compressor builds to 120 lbs and cuts off until it returns to 90 lbs then cuts back on and starts to rebuild. It holds pressure well and no leaks can be found.

Comments for Bus compressor will not build pressure between 60 & 90 lbs

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Feb 21, 2017
Bus compressor will not build pressure
by: Doug in s.d.ca.

Does it just run the brakes, or an airhorn or other device?

You say no leaks, how does it get below 90?

Is the spit valve closing reliably?

If all that is OK, then maybe the unloader is sticking open.

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