I have a 2002 Sport Trac and it just recently started blowing cool air instead of heat.

 

Ready?

• make sure fluid is topped up in rad, cap secured
• Bring engine to operating temp.
• feel upper rad hose, should be hot
• move temp control to MAX
• feel hoses entering and exiting cabin heater(under hood, close to fan)both should feel hot.
• if both cold, check vacuam hose on bypass valve.
• if one hot the other cold, back flush cabin heater core.

Report findings.....

 

Thanx Aqua, I checked upper hose. it stayed cold the whole time. The lower hose became warm. vacum hose seemed to be working fine. The funny thing is that it beagn blowing a little warmer then yesterday. I ain't very mechanically inclined. I assume I have a thermostat that may be going bad. If so, should I have the water pump replaced while they are in there. It has 58,000 miles on it and never had major probs. Oh, I have no idea about how to back flush cabin heater core.

 

first check the antifree level. if temp comes and goes, the water level is low, or thermostat is stuck... next, what is the dash gauge doing? low temp or random temp means stuck thermostat... no, you dont need a pump with a thermostat.

 

Hey Smokingun,
I need ALL the questions answered to make intelligent suggestions, there are no shortcuts. You must perform ALL the tests and report back individual results.

With the top radiator hose cold, how long had the engine been running?
If the top hose remains cold you have a circulation problem, what was the running temperature of the engine, H or C?

When you move the heat control Cool-Hot-Cool in the cabin the bypass valve should open and close, when it is opened the hoses to the heater core should recieve hot water.

There is no need to install a pump if the thermosat needs replacement.

 

Occum's razor, make sure the fluid is topped off. Then go from there. That is the most common problem as you describe. Top it off, drive it, check it again.