Why would the heater not put out any heat until it is cranked up to 90 degrees? on 2005 Hyundai XG350

The blower works just fine and so does the A/C and defrost. But hot air won't come out of the face and feet vents unless we turn the heat up to 90 degrees. We just started noticing this as the temps outside got cooler and we are getting more rain.

by in Marysville, WA on November 08, 2013
1 answer 4 comments
ANSWER by on November 08, 2013
Does the heat come out the defrost?
COMMENT by on November 09, 2013
Heat does come out of the defrost vents when we turn the defrost on at any temperature, but not out of the main vents and foot vents unless the temp is set to 90 degrees. We were wondering if it was the thermometer in the car's computer that was malfunctioning. The heat worked fine last winter, but we hadn't used the heat function since around June. I bought the car from a friend just over a year ago and other than replacing the original battery, haven't had any problems until recently. We also have to replace the pump motor for the windshield washing fluid.
COMMENT by on November 09, 2013
If this is auto temp controlled, there is a inside temperature control sensor that might be faulty, not allowing the temperature to rise until you override the system to demand more heat. The defrost works anyway. If this persist it needs to be tested with a scanner that can read the HVAC system to verify what the computer is seeing, and repair the malfunction.
COMMENT by on November 09, 2013
Any idea how much it might cost to get it repaired? It isn't an option under the estimator tab.
COMMENT by on November 09, 2013
It first needs to be scanned/read to see if sensors are reading correctly, or if actuators are moving properly. Once the reason for fault is verified, then the answer of price can be answered. A temp sensor is not very expensive, but get it read, by a qualified technician, then we can talk price.