Re: pressure switches

[jlandry@domain.elided (John A. Landry)]

Jim Grammer <jimg@domain.elided> scribbled in the sand:

>Thanks for the laundry list, John. Looking at the pressure switches in 
>Grainger, I see that part #2FG79 is the same spec's as your 5B419 with an 
>additional feature of 'unloader'. Wouldn't that perform the same function 
>as the seperate unloader valve?

I saw that too, but I'm not sure how that would work.  *If* the pressure
switch had two ports, then I might understand better.  Ya see, if the pressure
switch only has one port (like mine) how can the pressure switch "unload" the
air pressure from that single line and yet still know when to activate the
compressor clutch?  You could ask the Grainger store, and if they can't answer
such a technical question, they will give you a telephone number you can call
to get additional information.  They have product specialists available to
answer such queries.

>It seems my next question may have answered the first. I didn't see a 
>seperate check valve listed, but looking at the description for the 5A703 
>unloader valve I see 'Eliminates the need for pressure switch unloader and 
>receiver check valve'. Altough it doesn't specifically say so, I'm assuming 
>there is a check valve in this unit.

Yes... it *is* a check valve and unloader in one.

>If I've got this right, one could use a pressure switch w/unloader and 
>check valve combo, OR a pressure switch with a combined unloader check 
>valve. Correcto?

I presume so... would make a nice tidy installation.  Please let us know what
you find out about the Square-D combo switch.

>Also, any thoughts on a circuit breaker/fuse value for the 12v supply?

I'm measuring approximately 3.0 Ohms of resistance across the magnetic clutch
on my IH York compressor.  So assuming a nominal 13.7 vehicle voltage, that
means about 4.5 Amps of current flow through the clutch.  Thus, a minimum 5
amp rated switch or higher (or appropriate relay system) and fuse should take
care of things.  The fuse should be sized to protect the weakest link in the
circuit... probably the switch.  I have a little lighted toggle switch under
my dash, and I'll confess to *not* having it wired through the ignition
switch, so it can be activated whether the engine is running or not.  I didn't
want to add an additional 4.5 amp load through the ignition switch and I was
anxious to finish the installation job with the parts I had on hand at the
time.  I intend to add a cheapness relay under the dash to handle this, but
for now I'm just careful to turn the switch off after using the compressor.
Besides, because it's lighted and hard not to notice.  Just another item on my
long Scout "to do" list.

This holiday weekend is for rewiring projects!  I intend to replace my
headlight switch (a five minute job) then replace and rewire my front
headlight bulkhead connector located just to the left of the power brake
booster (several hours of work).  At the same time I'm going to wire in one of
those heavy-duty Napa dual headlight relays into my headlight circuit so the
full headlight current doesn't have to go through the headlight switch.  I'll
take care of the compressor switch needing a relay and lastly replace my
Traveler's travel top rear cargo light switch.  Whew!

Merry Christmas to all my IH owning friends.

John
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jlandry@domain.elided             |
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