Pipe on the roof of some EMD models

The GP-9 has a ... I'll say "coil" ... of pipe on the roof of the long hood: two side-by-side lengths of ... 3-inch? ... pipe, connected by a U-bend at one end. Similarly, the F-9 has a coil of this sort on its roof, which is not there on the F-7 or... well, there are no "F-18" to compare. (The second order of FL-9 for the New Haven have the 1800 horsepower engine of the contemporary GP-18, and so could have been called the FL-18. I don't know whether the two orders differ in regard to roof-top piping.)
QUESTION 1: I've assumed that this pipe was a cooling radiator for the air compressor. Is this right?
Today, on the display layout of the Edmonton Train Collectors Association (Bonnie Doon Shopping Mall, Edmonton AB), I saw an O-gauge Union Pacific passenger train pulled by an A-B set of ... well, E-8 or E-9. These units had (molded in the plastic of their roofs) what looked like similar pipe coils: one on either side of the rearward set of radiator fans.
QUESTION 2: Are these in fact the same sort of appliance as the GP-9 and F-9 rooftop pipe coils?
QUESTION 3: The E-8 being of the same generation as the F-7 and GP-7 and the E-9 being of the GP-9 and F-9 generation, is the presence of these pipes a sign of an E-9 (a spotting feature if you ever see one in overhead view)?

Well, I can give an answer to #3. Not enough people photograph trains from bridges over the tracks, so it is hard to get a view of a locomotive roof "outdoors" as you can looking at an O-gauge model, but I've found a reasonable number of fairly high angle photos of E-8 units (at "Fallen Flags"), and it looks as if E-8 as well as E-9 had "coils" of pipe on the roof, in the same position as those on the O-gauge models I saw earlier: beside the after set of radiator fans.
#1 and #2 anybody?
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The "Fallen Flags" site also has a bunch of operator's manuals for various diesels, and these have "general arrangements" diagrams. One for an E-9 has ... well, not a clear picture, but at least a number beside the rear radiator fans in abut the position of the pipe coils. And explains it as the location of an air compressor after cooler. Suggesting that, at least on E-8 and E-9, that's what the pipe is for.

I found part of an answer in "all about F's" by Dan Dover. See Extra 2200 South January 1970 page 19. Dover calls these pipe's aftercooler air coils on roof. And then states that they are original or with rebuilding. The UP "F9s" come to mind as rebuilt from F3s and F7s.

Ed in Kentucky

Thanks, Ed!
(I've never seen that Dan Dover article: I have a few old "Extra 2200 South" issues, but my earliest is a 1973 issue.). I was fairly sure the pipes had to do with cooling the air compressed by the air compressors -- steam locomotives often had visible piping for this purpose -- but it is good to get confirmation.
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You'd think, given the frequency that model railroads are viewed from above, that the model railroad magazines would pay close attention to roof-top details, but the "Model Railroader" articles on "phases" of F-units don't mention the roof-top coils. (Sniff.) But a "Railroad Model Craftsman" article from (I think) October 1972 on the New Haven's FL-9 units notes that only the first (1956) order (2000-2029) and not the second (1960) order (2030-2059) have the rooftop coils. They really should have been called "FL-18"! (Grin!) The New Haven gave the two subtypes different class designations: EDER-5 for the first order, EDER-5a for the second.
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Thanks again!