M35A3 air buzzer and warning light question

[187]

I have been searching the forum and TM's all morning Looking for a little added advice.

My truck will reach 120 PSI quickly and maintain pressure during driving. I have not found any air leaks, etc. so far. When I start the truck and the pressure is below 60 PSI the light and buzzer do not work. Both worked when I bought the truck about a month ago.

I was trying to determine what the issue was yesterday. I checked the connection at the air buzzer. It seems to be plugged in and I attempted to unplug it to check the connector and it was very difficult to unplug. I didn't want to force it so I left it as-is for now.

I removed the red bulb and and plugged another dash light bulb into that socket and discovered that the bulb was barely lit....like low voltage?

Does the light get it's power from the buzzer? Or another source?

Is there only the one connection to the buzzer (the black wire that goes into the bottom of it)? Does that wire simply pull out?

Any suggestions appreciated!

 

[porkysplace]

This may help you.

 

[M35A2-AZ]

I would start at the pressure switch and work your way to the problem.
You could have a bad pressure switch bad wiring or a grounding problem.
Look at the wiring drawing and find out were the power enters the circuit.
I would think it starts on the pressure switch side, but I am not sure.

 

[Deuce007]

I had this same problem also but I found the problem on mine. under the steering column right behind the large hose that comes from the heater there is a hose that sometime comes off. In the picture attached shows what it looks like when the hose isn't connected. I marked both the hose and where the hose connects to with a red dot in the picture attached if they aren't connected neither the air buzzer nor air warning light will work. hope this helps.

 

[187]

Update

Thanks for the suggestions so far!

I unplugged the buzzer and the light now works when less than 60psi of air is present. Turns off with more than 60psi.

Does that mean the buzzer is bad? Maybe causing the light to short out when it's plugged in?

 

[187]

Also, is the A3 buzzer different from the A2? I will get a replacement, plug it in and see waht happens....

 

[clinto]

This may help you.

That's the A2 schematic-poster has an A3.

 

[KaiserM109]

That's the A2 schematic-poster has an A3.

It's also for a gasser, but I'll bet a lot crosses over. Oops, that spark plug is part of the manifold heater. My bad.

 

[Rustygears]

Interesting problem. Seems like you're describing a big voltage drop across the pressure switch, even with the buzzer disconnected. From the description, sounds like the switch contacts are fried or dirty. Time to replace or refurbish.

 

[187]

Ok an update.

I finally got around to getting a replacement air buzzer. I plugged it in and at least the replacement doesn't cause the low air light to go out. But the buzzer did not work.

I put a meter on the wire that goes to the buzzer. The meter reads 24V until the truck builds 60PSI as it should and then cuts the volts to zero after 60 PSI. The red low air light also works as it should, turning off after 60PSI.

Do you think I have a defective buzzer? The one that is mounted in the truck causes the red low air light not to work regardless of PSI and the replacement I received does not sound, but does not cancel the low air light. Strange. I believe the pressure switch is working correctly since the light functions and the voltage to the buzzer is correct.

Thoughts?

 

[moving chicane]

Sounds like a bad ground at the buzzer, or less likely the black wire is damaged at some point allowing you to show 24V and enough amperage to illuminate the light, but not operate the buzzer. This could be checked by observing for fluctuations on a test light while wiggling the cable at different points along it's length. Definitely clean the grounding points and apply some dielectric grease. You should be able to check the buzzer function with a test lead and your batteries.

 

[187]

Finally got around to getting this fixed. Took the pressure switch out, cleaned it, blew it out with some air, and cleaned the two plugs/connections. Worked like a charm. Now the buzzer and light work. Close quarters in there! Thanks for all the suggestions.

 

[SRB1976]

Finally got around to getting this fixed. Took the pressure switch out, cleaned it, blew it out with some air, and cleaned the two plugs/connections. Worked like a charm. Now the buzzer and light work. Close quarters in there! Thanks for all the suggestions.

I'm having the same issue. Where's the pressure switch located?