No air to secondary tank... pressure stays at 50 at idle RPM's... please help!

It could be anything, including a faulty gauge or sensor. Do you hear air leaking?

Also bypassing the dryer isn't a smart thing to do. For emergency situations, bypassing will work to get it to a place to have it fixed... If you truely are a Mercer Driver, then bypassing the dryer will give you an automatic failure of you 6 month inspection cycle. Perhaps you have a bad dryer cartridge. I'd change that first before trying to bypass it. They only cost about 30 or 40 dollars & really should be changed on a bi-annual basis if not anually.

 

Had a similar problem and it was the Regulator, 23 bucks and I did the labor myself. Fixed

 

I was going to mention the govenor. The spring could be wore out and it's partially unloading instead of pumping.

Another possibility is all air compressors have a filtered air inlet. Most big trucks the air inlet is hooked to the engine air filter. Check the filter, it might be dirty or the air inlet tube might have trash in it restricting the air flow to the compressor. Increasing rpm's increases suction so it might be?

 

or the load check valve located in the head on compressor.

 

If one tank is filling to governor set pressure and the other is not, there is a double check valve between tanks that prevents loss of air from the primary tank if the secondary blows and visa versa, it is likely stuck, drain both tanks then rebuild air and it should reset or replace it

 

If Both tanks are building slow, I have seen carbon buildup in the air line from the compressor to the air drier, the first section, 3 feet or so is metal brade or copper because of the heat, then a brass fitting then regular air line to the drier, that fitting can get plugged with carbon. All compressors pass a bit of oil, combined with the heat it makes a carbon like residue that can be hard as a rock, it can collect in the restricted area of the joiner fitting mentioned above and severly reduce air flow.

 

Thats it! I could not think of the right terminology. you need a unloader kit, it comes with a gasket. comes with new springs & the thing a ma jig's. about 12- 18 bucks.