Yes but it wouldn't hold.
Sounds like the air wasn’t built up enough to hold the trailer brakes. When you’re doing your pre-trip, and you set your brakes, meaning red valve (trailer brakes) in and hand valve engaged (valve down), you ALWAYS keep your yellow valve (tractor brakes) pulled out.
Anytime you step out of that tractor, always, ALWAYS, pull the yellow valve out, setting the tractor brakes. If you don’t, you’re gonna have a rollaway.
With very few exceptions, the only time your red valve will be out is when you are getting ready to separate from the trailer.
When you’re doing a pre-trip, the red valve is in, yellow valve is out and the hand valve is down. You do this for three reasons.
One, yellow valve out, to keep your equipment secure, because the tractor brakes are on.
Two, red valve in, turning on the air to the red lines, which controls the trailer brakes. You do this to check for air leaks on the red glad hands, lines and brake chambers.
Three, you drop (set) the hand valve, which is part of your service lines, same as your brake pedal. These are your blue lines and blue glad hands. This engages the trailer brakes and all of your brake lights. This lets you check for air leaks in your blue glad hands and lines, and your brake lights.
The hand valve is also used for your very last check, which is, you put it in drive, drive forward a few feet and drop it. This is to check that your trailer brakes are working. Your trailers should abruptly stop. If they slowly stop, you can still drive with them, but they should be red-tagged when you get where you’re going as, “slack adjusters need adjusting.” If the trailers don’t stop at all, then, obviously, your trailer brakes aren’t working, and you need to go to shop.
One more redundancy an old-timer showed me, is during the pre-trip, when you’re at the back trailer, turn on both of your valves below the the glad hand connections. You should hear air hissing. If not, you forgot to turn on your air, either in the cab, or at the front trailer.
I do this all by muscle memory, but typing it, I’m hoping I haven’t overlooked anything. But just remember, yellow valve out, red valve in and hand valve down. And if your hand valve won’t stay down, write it up.