Bud Backer

There may be a lingering bug affecting setup of MGs in buildings, so watch out for that. 2 minutes is normal, but if they go into a deploy "loop" (where they reach end of deploying cycle and then start over) for more than 2 minutes, it is a bug.

As per YankeeDog's suggestions, don't forget to actually DEPLOY the HMG. Some HMGs can fire without being deployed (You'll see a semi-deployed status) but their accuracy suffers greatly. Also, IIRC, HMG deployment in buildings takes a little more time to setup than normal, this may be why your teams aren't firing. If you keep issuing movements then you reset the deployment time.
 
Here's a link to an old thread regarding the issue of deploying in a building - One guy recommends not using the Arc command when deploying as it tends to break the TacAI.:
 
http://community.battlefront.com/topic/110940-hmg-in-buildings-bug/?hl=%2Bdeployment+%2Btime#entry1465868

During setup, don't worry about whether the HMG team is exactly in front of a window or not; the visuals aren't 100% WYSIWYG.  Rather, DEPLOY the HMG team into the building, and then check what areas they can target using the TARGET command.  Blue line = they can see and target the point where the cursor is.
 
Bear in mind that the TARGET line is intentionally somewhat conservative; units will sometimes be able to spot and shoot at enemy units beyond what the target line shows, especially in areas where you get the "Reverse Slope No Aim Point" alert.
 
If the MG's field of fire isn't to your liking, use the FACE command to change their deployment inside the building, and try again.  During setup, deploying HMGs in buildings is instantaneous so you can play around with FACE as much as you please. You'll sometimes find that fairly small changes in facing have a dramatic effect on LOF, so it's worth playing around for a while and even trying some FACE orders that are as much as 90 degrees off your planned vector of engagement.
 
Any way you slice it, though, there are usually limitations on the field of fire for an HMG in a building. This can be a good thing as a limited field of fire goes both ways -- it also limits the locations from which an enemy can directly fire back upon the HMG.  But if you want a really wide field of fire from a building, for HMG types that are allowed to fire "semi deployed" such as the MG42, you may actually want to leave the HMG only semi-deployed in the buildings so that the gunner can move quickly from window to window in order to engage new threats.

I will try your suggestions but what do you do when you are in the deployment phase and want already established HMG positions? There is nothing to target, and it seems to me that one might actually not want to have them open up until I make the decision to reveal them. Trouble has been at that point they just squirm around the room and do nothing.
I have given them a move and target order in the past but it got nothing out of them until I gave up and ordered them to exit the building and deploy outside. Then, they were quite happy to shoot. That suggests the problem is not with my clicking but with how I handle them in buildings. I see your point about partly ruined buildings but this was not the case in any of my scenarios.

Edit: accidentally upvoted myself.

I find the most effective way of getting HMG crews to set up so they can fire out in a given direction is to actually assign them a specific target order at the end waypoint. Next best is to give them a Target Arc, but Face usually suffices. Sometimes, though, it just turns out to be too difficult to do on the tactical timetable. Whether this represents reality (the MG needs something fairly steady to sit on; perhaps the crew can't find anything to hand to raise it over the sill, or the floor is all gone and they can't just sit it on the exposed joists and expect to be able to fire it.

So I did a 30 minute battle, American assault on a tiny map. The single US vehicle was an M10 TD that came charging out the gate shoring up everything in sight. I had a PAK completely across the map and was a bit worried this might go badly, Then the schrek team you see im the foreground, the one I expected to get chewed up by the infantry accompanying the M10, popped up, and took two shots. The second one killed the M10. I liked the perspective shot here, shooter close to the "camera" and the target in view in the distance.