I just had all the hardware replaced on the HHR, but the front left brake locks up completely..... It is very hot at that point.

The mechanic is telling me it's the proportioning valve, but I am skeptical. Ideas ?

 

Either the brake hose has been damaged or the caliper piston is sticking, most commonly due to the slide pins not installed correctly or lubricated properly.
I did a repair a few weeks ago the rubber ring on the top caliper pin was stuck inside the caliper, after some brake clean spray and use of my dental hook, I got it out. Then I replaced it with new pins.

 

Find a new mechanic. The proportioning valve only exists on non-ABS HHRs and then only affects the rear wheels.
I have never heard of a proportioning valve going bad; I don't think they even have moving parts.

 

Someone posted about the brake hose kinked.

 

The Chevy dealer found that the first mechanic had put a defective booster on and that was causing the issue. It is all good now and the HHR is back on the road... Thanks for all the feedback !!!!!

 

I’m sure he didn’t install it intentionally, stuff happens, it’s all good now! Enjoy the ride!

I did wonder, you stated you had new hardware installed, to a new brake booster is a component, nuts and bolts pad pins are hardware. Just saying.

 

Done a lot of brake jobs, never have I've seen a brake booster lock up one caliper.
The booster gives brake assist to the complete brake system.
Somebody is snowing somebody.

 

I agree.

 

Maybe it was the master cylinder, it’s attached to the booster

 

Correct me if I'm wrong.
The HHR has a 4 channel ABS system.
Both master cylinder lines goes into the hydraulic control modular, two for the front brakes and two for the back.
Can't see how a master cylinder can cause one wheel to lock up.
I would say if the hydraulic control modular has a problem for the front brakes it could cause one caliper to stick.