GM Truck Club Forum banner

vacuum pump??

2010 Views 7 Replies 2 Participants Last post by  Asphalt Animal
I just got a 95 silverado with a 6.5 turbo motor. The a/c didn't work so I've been working on that. Got it so it blows cold now but there is another problem. When I turn on the a/c the vacuum pump does not turn. I have changed the belt and belt tensioner. Could it be just my pump is going out? I noticed when I was driving it that the check engine light comes on and will go off some times. Is there a way to chek the pump?
1 - 4 of 8 Posts
Check your codes first! The '95 is still OBD1 and you can check the codes with a paper clip grounding out the A & B terminals on the diagnostic connector, turning the key to ON (DO NOT START IT!) and reading the codes as they flash. You should get a code 12 to flash 3X, then it will proceed with the next code(s), each flashing 3X. Write them down and find out what they are. If there's a problem w/ the vacuum pump you will likely have a boost code stored. If you are losing vacuum from the pump seizing, you should be losing boost and possibly see black smoke coming from the exhaust as this happens; especially under load.

Being that the pump isn't turning, it can certainly be bad. Remove the belt and see how it spins, it will get stiff as it spins, but should then loosen again.... If it is actually binding, it's shot.
The pump pulley is going to appear polished at some point in time just from use. Be sure when you R&R the pulley you find the right tool for doing this. GM had a tool for it as if it pressed on with the tool, not in an actual press.
Not seeing just how the pump is, I can't say that is or isn't bad. It may not be if it was creating enough vacuum previously. I'd certainly say it may be worth trying to break the glaze off of the pulley and make sure that when the belt tensioner is against the belt it's not at the end of its travel. Belts will stretch a bit, and if the tensioner has reached its limit, it simply isn't going to hold it tight enough.
Good to hear you're rollin' again!
1 - 4 of 8 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.