My heater has no cold. I didn't have room to fit the heater control valve, but found that if I directed the air to the windscreen and shut the vents there was no/very little heat coming through.
It's worked very well for 3 years until my recent holiday to Croatia. Driving through Italy in + 30°C Mrs Verbose was seriously complaining and her flip-flops were breaking down in the heat. Even I was baking a bit.
Not having any tools to divert the hot water, I instead took off the pipe from the heater to the cabin and then blocked the cabin pipe with a pair of my pants and a plastic bag.
The relief was tangible.
Yes, they were used pants, but I couldn't smell them. 
Lucky I wasn't wearing my black leather studded posing pouch.
I'll order a couple of valves so I can have 'summer heater mode' and 'winter heater mode'.
