How much damage did I do?

[JohnHere]

When done checking pressures, I relieved the high pressure hose back into the system through the low side to minimize 134a loss; however, I did not first purge the manifold lines of air.

Backing up to your first post, the only way that procedure works is if you first evacuate and then re-charge the system. This way, you'll have nothing but refrigerant in the Manifold Gauge Set hoses that can be drawn back into the low side of the system free from any air. Testing the pressures in an already charged system with a MGS can be done with minimal loss of refrigerant, presuming that you do so only a couple of times.

[nvacnoob]

When done checking pressures, I relieved the high pressure hose back into the system through the low side to minimize 134a loss; however, I did not first purge the manifold lines of air.

Backing up to your first post, the only way that procedure works is if you first evacuate and then re-charge the system. This way, you'll have nothing but refrigerant in the Manifold Gauge Set hoses that can be drawn back into the low side of the system free from any air. Testing the pressures in an already charged system with a MGS can be done with minimal loss of refrigerant, presuming that you do so only a couple of times.

That is good to know, thanks! I had read that the high pressure hose on the MGS could potentially hold 3 ounces of refrigerant, so I followed the procedure of moving that hose contents over to the low side, and back to the system. Hindsight, I should have just disconnected after checking, putting nothing back into the system, especially since I was using a rented MGS. Technically, I don’t know what a past customer could have put through that hose, so I guess there’s a risk of additional contamination to my system. When I do the job, it will be with a new MGS.

[JohnHere]

I had read that the high pressure hose on the MGS could potentially hold 3 ounces of refrigerant, ... .

Depends on how long the hose is. For all practical purposes, with 3-foot-long hoses on a rental Manifold Gauge Set, I doubt that the HP hose would hold that much refrigerant. One-half ounce, maybe?

[tbirdtbird]

I measured the amount of liquid left in the hi side hose once. 6 ft hose. I got 2 oz.
Be aware that if you do not bleed the hi side hose back into the low side, given that the hi side hose has liquid under pressure, when you loosen the knurl nuts the remaining refrigerant will flash and you could burn your fingers or your eyes. Better to bleed it back to lo side, IMO

[nvacnoob]

My rental gauge did have 6’ hoses…