overwhelming heater valve?

[72-k20-burb]

For those who have put an LS in their rig, do you have a higher fail rate for the heater water valve?

(The vacuum controlled one that keeps hot water out when using AC.)

Reworking my AC system in the burb with rear air, it took over 5 lbs of r134 before it got cold.. Now it's condensing, cold in back, hot up front. So thinking valve is bad again, sure enough hot on both sides.

I've had three of these seemly go bad, and very quickly. Two of the brass OG style ones, and one plastic newer one.

Do LS water pumps push too hard for these to survive? Not opposed to installing a manual valve to keep it closed, but in Southern CA sometimes you need heat defrost in the morning and then AC the rest of the day. Not ideal to pop the hood but I'll do it if needed!

I have confirmed that prior to fail these are closed when vacuum is applied, which is the way my AC is currently set up.