2003 TL Climate Control Temp Problem

[DriveOnBy]

2003 Acura TL - No Nav or S

My climate control system is not working properly. Both A/C and heat work, but smaller changes in temperature from cooling to heating only changes at the upper and lower ends of the temperature settings(not all the way to the max overrides). When cooling, it is necessary to turn the temperature up to the high 80s before any heating occurs. Once the heating starts, it won't stop until the temperature is turned into the lower 60s.

Checking and testing the various components I have found that each component works, heater valve and cable move freely, and there is no issue with the coolant levels or blocked core. Air mixing doors operate normally.

The problem is that the heater valve is not actuated incrementally. I does not attempt to operate until the temperature is set very high, then it opens fully. It does not attempt to close until the temperature is set very low, then it closes fully, with no in between.

The air mixing doors move incrementally as expected smoothly without any ticking/clicking or twitching. Is the heater control valve not operated by the air mixing motor? What other than sticking valve/cable would cause it to not actuate the heater valve incrementally?

Thanks in advance.