Cycling Compressor?

I have a 1991 Cherokee with the I6. On the passenger side firewall there is some sort of compressor or something that cycles every now and then. It's pretty loud and usually cycles for about 10 seconds or more when I go to start the Jeep after several days of sitting. It will also intermitantly cycle when the Jeep is running. At first I thought it was the fuel pump, but I now know that is not the case as the fuel pump is in the gas tank. The location again is on the passenger firewall below the silver a/c line box and that little "shelf" that is flat like a battery tray. It's not down low like the blower motor. I really didnt get to see what kind of lines were coming ot of it or where they went. I'm curious to know what it is and why it cycles like it does. Any thoughts would be appreciated. Not at home right now or I would post a picture of it.
Thanks

I don't have a '91 but ... do you by any chance have ABS?

yes I do have ABS..and as a matter of fact the abs light in the dashboard is constantly on. I know its not working because I can lock the wheels up at any time. My friend who I got the jeep from brought it to his mechanic regarding it and he said that the brakes worked ok and to start searching as to why the light is on wouldn't be easy on his wallet so he left it alone. DO you think that it has something to do with the ABS. I thought all the ABS stuff was on the drivers side. I will go outside and take a picture of wha I am taliking about and post it.
Thanks

there ya go...when you start the rig you hear the noise because what it is supposed to do is regulate pressure for your brakes. IF it is doing it while your driving it doesn't have the "right" amount of pressure for the pump to do its job.

You could...

A. Find a new / used ABS pump or...
B. Pull the fuse on the ABS system and have regular brakes like most of us.

C. New ABS pump is NOT cost effective.

Here is a picture of what I am talking about. Thanks for your help.
http://img43.imageshack.us/img43/492/compressor6um.jpg

Thanks for the reply. You are right about being cost effective. I got the Jeep for $0...It just needed a water pump.

Do you suggest that I pull the fuse. That would stop it from cycling. Would it get rid of the light or do I need a piece of tape for that light.. lol

Nuff said:

Thanks for the reply. You are right about being cost effective. I got the Jeep for $0...It just needed a water pump.

Do you suggest that I pull the fuse. That would stop it from cycling. Would it get rid of the light or do I need a piece of tape for that light.. lol

Click to expand...

Yeah...pull the abs fuse from uder the PDC (black rectangular box, passenger side, under hood,marked ABS fuse. Probably 60 amp ) You can use tape...but you can also remove the bulb.

Thanks again for the reply. Will pull the fuse tomorrow.