Auto Heater/AC Control Unit Failing

[Jason]

All,

My Auto Heater/AC Control Unit keeps going dark on me. No lights, no fan, no temperature control, no actuator control. I have tracked it back to the relay in the engine fusebox labeled EB-25 Heater. It's also labeled X-6 in the shop manuals. I have blown that relay about 4 times. At $35 each or $5 each from my local U-Wrench-It, its getting expensive and the supply is running low. All I can find and understand in the shop manual is that if the relay is bad, replace it.

By the way, when a new relay is installed, everything operates fine. However, the last relay lasted about 5 minutes.

According to the schematic, the electricity flows past fuse EB-5 (which is good) then through a wiring harness to Intake Actuator. From there it flows on to the Auto Heater/AC Control Unit in the dash.

Where do I troubleshoot from here? Is my control unit bad? My Intake Acuator? Or is it something all together different?

Thanks,

Jason

[SilverBullet75]

If the a/c compressor is having issues it can cause the fuse to blow. Possibly the relay too?

[bartmanS4]

Can you tell what the failure in the relay is? If it's the coil burned open then it's getting too much voltage which doesn't seem possible without many other issues cropping up. Are the contactors burned or stuck in one position? This could indicate something in the circuit drawing too much current. I don't know how much current should be present but you could measure it or have someone do so and compare it to another VX. If it's running high current then one of the components along the line needs to be replaced - not very specific I know.

[Jason]

The relay is a simple black cube with five prongs. I am unable to see anything on the inside. On each of the relays that has burned out, the plastic housing at the base of the prong, is melted and slightly bulging. I can't see the position of the relay. However, I did put a voltmeter on it and checked for continuity across the prongs. I found that the continuity was the same on a good relay as it is for a bad one. Makes me think the bad relay is "frozen" or "burned" into it's normal position and unable to switch to the position it is supposed to be in when an electrical charge is applied. In other words, I have no idea what I'm talking about.

Does my description tell you anything?