mcratchet1 Posted June 28, 2019 Share Posted June 28, 2019 Ok so i have a 2006 mack mr688s vin# 032711 always would pop air out of purge valve every 10-15 seconds all day Air compressor went out so installed reman from mack as well as a new air dryer, governor, and new air line from compressor to dryer still popping off every 10-15 seconds could someone help a brother out on this? i have never had one do this thanks in advance!!! Quote Link to comment Share on other sites More sharing options...
Mack Technician Posted June 28, 2019 Share Posted June 28, 2019 (edited) Follow you air governor line back to the tank its sensing pressure from. That's your wet tank. Wet tank gives air to both sides of your trucks air system and never takes any back. Wet tank has no monitoring, so temporarily screw a gauge in an open port on the wet tank so you can see what's happening there. Wet tank is isolated and is a relatively small cavity, 1/2 a tank in size, usually a split tank at low position. The governor only senses your wet tank since it's the supply to trucks air system, governor can't tell you what the rest of the system pressure is, it's only function is to make sure the wet tank is always full so rest of system can be fed off the wet tank. Scenario.... 1. Governor properly/accurately senses the wet tank....which (tank) is going low on air constantly - so fix origin of the wet tank leak. Your dash can't see what's going on at the wet tank either, so put a gauge in it. 2. Governor has lost its mind and is failing (AKA- Gavin Newsom syndrome). It's new, but that doesn't mean it's good. It was a topic the other day on here and I also had a new one that was bad out of the box last fall.... right from Mack dealership. 3. Any line leading to and away from the governor could be leaking off the signal governor is trying to send. For example: Governor can't send a large volume of air to a leaking spitter valve to unload it, or a leaking sensing line, or a leaking unloader in compressor head (which yours is new, so don't worry), governor can't compensate for the leak by sending more air fast enough and then you get a "drop out"..... a repetitive cycle of loading and unloading. Get soapy water and check while running...every sensing/control line. Note: I also only got one year out of my AD9 split valve and it blew out a seal causing wet tank leak down out the bottom of the dryer. crumby parts. Edited June 28, 2019 by Mack Technician 2 Quote Link to comment Share on other sites More sharing options...
Ezrider Posted June 30, 2019 Share Posted June 30, 2019 can't really add much to your post mach technician. most times i have come across that it was normally a leak in the sense line from the governor to the wet tank or a leaking fitting on the wet tank. Quote Link to comment Share on other sites More sharing options...
Rob Posted June 30, 2019 Share Posted June 30, 2019 I had an AD-4 on one of my Mid-Liners and the air dryer purged five times every cycle. Strangest thing in rapid succession, psss, psss, psss, psss, psss, and then stop. Turned out to be a hairline cracked brass compression fitting on the sense line at the dryer port. Finally found it with soapy water and variable pressure shop air plumbed into the drain port of the wet tank to test the complete system. Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
mcratchet1 Posted July 1, 2019 Author Share Posted July 1, 2019 Ok thanks for all the help!!! I'm going to check it out today Quote Link to comment Share on other sites More sharing options...
mcratchet1 Posted November 7, 2019 Author Share Posted November 7, 2019 so getting back to this, i have checked ever where for a leak cant find one truck holds air pressure over night also Quote Link to comment Share on other sites More sharing options...
Quickfarms Posted November 8, 2019 Share Posted November 8, 2019 Is it holding air in the wet tank or by the dash gauges?I I remember correctly there is a check valve on the inlet to both the primary and secondary tanks on the feed lines from the wet tank Quote Link to comment Share on other sites More sharing options...
mcratchet1 Posted November 8, 2019 Author Share Posted November 8, 2019 yes from dash, ill take a look at check valves should i put a gauge on the wet tank itself to see if its losing air somehow? could it backfeed thru a valve? Quote Link to comment Share on other sites More sharing options...
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