My climate control suddenly goes full hot; why?
NOTE : At WOT (Wide Open Throttle) the A/C will cutout to prevent damage to AC components. If you're driving everywhere in a hurry, don't try to fix a nonexistent problem. ;-) A common failure point on SHOs that can cause this symptom is the "blend door actuator"; in particular with cars equipped with the Automatic Temperature Control (ATC). A weak or dying car battery can sometimes also be the cause as it messes with the EATC head unit's "head" (so to speak...) due to low voltage.
To determine whether the blend door actuator is faulty, run an HVAC systems self test on your SHO. A code of "02" = Blend Door. The cost of the part, FODZ-19E616-A, is not terribly expensive, any where from $51 (Lou Fusz Ford) to $100. The actuator is a little motor that moves the blend door open and close. It also moves it into in-between settings for a blend effect (cooler air or warmer air etc.) When the actuator fails completely one gets perpetually hot air blowing out of the vents no matter what the setting of the HVAC. (Probably a fail-safe situation.)
The cost of the part is the least of your worries. Installation is the problem and requires removal of the dash from the firewall of the car (or at least about 18" away from the firewall). Expect to have a Ford Dealer charge from $500 to $600 for the part and installation. If you do the work yourself, expect to take from six to twelve hours.
If your SHO is still under warranty, refer the dealer to TSB No. 94-19-8 from 09/21/94, titled "HEATER - ELECTRONIC AUTOMATIC TEMPERATURE CONTROL - BLEND DOOR WILL INTERMITTENTLY GO TO FULL HEAT POSITION." If your SHO is out of warranty, and you want to do the repair yourself, read on
One List member (with some assistance by another) described the work as follows:
- Unbolt the front seats and remove them from the car. Next, take the trim molding off at the front of the doorjambs and peel the carpet away.
- Remove the bolts that hold the dash to the body. Under the grills on top of the dash, there are screws to remove, also. The steering column is held by four bolts underneath the dash, remove them and let the column drop. Careful! Don't start pulling wires at random. Pull one major wiring harness on driver's side, antenna and harness on the passenger side. Now, look and see if anything else is in the way and only remove what is necessary like the (e.g., speedometer cable, etc.).
- Get a friend to help you remove the dash from the firewall. Don't try to raise it out of the way and work under it. The actuator is in the middle of the firewall and is on top of the evaporator and heater core case.
- Three screws hold the actuator in place, one of which is difficult to access. There are three ways to access this screw: First, cut the sound insulation above the actuator away. Pry it up. Pull on it every way you can think of. Cut it loose with a hack saw blade. Observe location of tab and screw on bottom of actuator. Second, read the manual. Pay special attention to the little arrow marked view A! Third, buy the replacement actuator. It comes attached to a bracket, which will make everything pretty obvious.
- Finally, check out the blend door shaft. Sometimes, it will sometimes show signs of cracking and wear. It's a little harder to replace, but wrapping some duct tape or Teflon tape around the shaft will tighten the shaft adequately to allow the actuator to function as designed. It's a good idea to clean the mess that can accumulate in the blend door case by vacuuming it out. (A possible reason for a bad actuator.) Assembly is the reverse of removal. You should not attempt this repair without the factory manual. Even with it, you need to do a fair amount of planning and interpretation.
If you don't have time, money, inclination, etc to properly fix the blend door - here is an alternative provided by Tim Montiglio.
If you need a quick fix during the warm season do the following:
- Make sure your SHO is off.
- Remove crap from glove box and pinch side retainers to allow box to swing down.
- If you feel around on top of the evaporator core housing behind the HVAC control head, you can touch the blend door actuator housing and the group of 6 or so wires coming from the acuator motor.
- Follow these wires down about 6"-8" until you find the connector. This connector attaches to the blasted control head. Disconnect the connector.
- The blend door should stay in whatever position it was (probably 72o) before the actuator failed.
Came upon this by necessity. When problem first occurred, I did the service manual check on the actuator and it tested OK. The manual flowchart pointed to the control head which is a $550 item. NoCanDo. I then disconnected the #249 lead at the back of the control head which jammed the blend door to full cold. I live in South Florida. This was OK for a few years until the acuator door decided to try and close itself to death. This sounds like a hammer hitting the firewall once per second. Thats when I figured out the total disconnect.
Another cause of the AC suddenly losing the ability to blow cold air is the AC clutch gap being out of spec. That's easy to check - see the Resetting the gap on the A/C clutch page. If your problem isn't the blend door actuator or AC clutch, you're likely low on freon - get a pressure check.