Emglo AirMate Model #AM78 HC4V Does not shut off

by Scott
(Indianapolis, IN)

Emglo AirMate Model #AM78 HC4V

Emglo AirMate Model #AM78 HC4V

Emglo AirMate Model #AM78 HC4V
Emglo AirMate Model #AM78 HC4V Pressure switch
Emglo AirMate Model #AM78 HC4V PRV

I'm sure this has been answered before, based on your introduction that indicates there are thousands of questions and answers but I can't seem to find it (the search box above searches the WHOLE INTERNET, not just your site, so I end up with computer answers and other non-relevent stuff). So I apologize in advance!!

I have an Emglo AirMate Model #AM78 HC4V that I inherited from my Dad, so I am not real familiar with it, nor it's history. It is marked "125 PSI" on a sticker but it is not shutting off when it reaches that pressure (on what I consider the "Primary" gauge, not the adjustable one at the air supply). It continues to build pressure and then what I call the "Pop-off Valve" blows and it drops pressure immediately and I shut it off manually via the manual ON/OFF switch.

I've included a couple of photos - one of the overall compressor, plus one of what I call the "Pressure Switch" and one of the "Pop-off Valve". In the pressure switch photo - I've outlined what I call the "Pressure Switch" in GREEN. I've outlined the "Pop-Off Valve" in BLUE and what I assume is some kind of "Sensor Supply Tube" in RED, which appears to supply air pressure up to the switch so that it knows when to shut off.

We were borrowing the compressor last year for my Son's Eagle Scout project and the compressor was working fine until the "Sensor Supply Tube" split (outlined in RED in the photo), so I replaced that with similar tubing from Home Depot or auto supply store - I don't remember, but it seems to be OK now...

Then, right away when we started using it again, my current symptom started - it builds pressure in the tank, but never shuts off and then the "Pop-Off Valve" blows at about 140PSI or so.

Just providing the above regarding replacement of the tubing for background, since I don't know if these two issues are related or not??? Maybe it wasn't shutting off properly and that's why the "Sensor Supply Tube" split in the first place (too much pressure before the pop-off valve blew??) or perhaps when the tube split, it has a diaphragm or other mechanism within the pressure switch that was also damaged or needs reset or replaced???

Anyway - I'm assuming that it's the pressure switch that's not functioning now, but is there a way to repair?? Or at least test to confirm before purchasing a new one (if they're even available for this old compressor)??

Thoughts? BTW - you have a very informative site here and I can't wait to delve into it more to better understand my compressors!!


Comments for Emglo AirMate Model #AM78 HC4V Does not shut off

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Oct 16, 2016
Emglo AirMate Model #AM78 HC4V
by: Bill

Sorry that the search boxes didn't provide help. There used to be a toggle that could restrict the search to the site the box was on, but that seems no longer to be the case.

The pressure switch tube (red) is the unloader valve line.

The blue circle is the PRV.

Visit the sitemap page for a list of all pages on the site, and also the troubleshooting page for details about issues that trouble multi-brand air compressors, including Emglo.

Off hand I'd say that you need to open the pressure switch, and carefully (live wires) use a multi-meter to determine if power is still crossing the switch points when the tank pressure goes past a normal cut out pressure of 125 PSI. Let the compressor run to 130 PSI and then test the wires on the motor side of the switch. They should not be live. If they are, then it is likely that your pressure switch is pooched.

See the pages on pressure switches for complete details about how they work.

Buy my ebook the Home Compressor for lots more info if you wish.

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