there a temp. control motor that control the a/c & heater replaced motor price is about $184.50 for the part
It could be the heater valve which is located under the hood to the passenger side down below the radiator and fan units.
Check the following........... 1. A/C heater control doors. 2. A/C heater controller. 3. Trash in the heater box. 4. Partly clogged up heater core.
Check the following items............... 1. A/C heater controller. 2. A/C heater controller doors.
MAKE sure that is the problem.If heater is blowing cold air,reach on passenger side,under dash,and find the heater blower,and gently pull the white plastic piece to make sure it is not stuck on cold.They go from hot to cold easily but not back to heat.
It is possible for hot air to be coming out of the driver's side and cold on the passenger's side if there is a dual temperature control on the heater/AC unit. Try adjusting the temperature controls to see if that fixes the problem.
Warm
That sounds like a blend door problem.
Possible causes are low anti freeze in radiator. Heater core could be plugged. Your dash controls may not be working. Plugged heater hoses.
You may have a stopped up heater core, or it may be a faulty heater door or heater door control. Answer: Check coolant level. Replace thermostat. Check heater control cable, located under small cover above the the passenger floorboard, near the console.
Has a bad blend doot actuator. It is under the dash near the ducts, and it looks very hard to change.
they lived in cold weather
I have a similar problem with a 2001 Grand Caravan Sport - Passenger side blows cold air at all settings. So far research has pointed toward a bad actuator and/or blockage of some type at or in the heater box. Haven't yet dug into it to confirm but I'll post once I have.