Hi everyone.
My ECC unit will not do anything sometimes early in the AM, usually when it's below 20F outside. No lights come on the unit. The buttons and knobs do nothing. 9/10 times during the year, the unit will work just fine. It seems to be only when it's below freezing outside that the unit doesn't even come on.

My thought is the solder joints are weak (or something electrical that's on the way to breaking) is exacerbated by the cold weather. Metal shrinks and all.

Anyone else have a similar issue? Been able to diagnose? Any suggestions for how to diagnose this issue to make sure it's the ECC? Ideas for taking it apart or replacing some common electrical component that fails?

I've been dealing with this issue for a few years. It's gotten worse as time has gone on. Since it only manifests when it's frigid out, I haven't bothered to fix it.

Thanks in advance for any help you can lend!
--
------

I would start at the fuse box and work my way to the ECC unit. The ECC box is usually quite well made. If you pull the radio out and rest it on the shifter, you can then yank the ECC box out of the dash to check the electrical connections.

Are both the blower speed and the vent selector in the "AUTO" mode? If so, the blower motor will not engage until the engine starts to warm up.
--
Keeping it running is better than buying new

Klaus!! So nice to see you still making the rounds on here!! :)

I'll take a look at the fusebox and look for suspicious things. I already have the ECC pulled and will open it up to inspect it for visible issues. The electrical connections on the ECC look clean and new.

When the issue occurs, there are no lights on, on the ECC. Moving it from auto to 0 to manual back to auto or any other permutation doesn't do anything. Moving the vent selector around also does nothing. I don't hear any electrical motors move as they normally do when the issue occurs. No lights turn on or change when I press AC on or off. Hitting recirculation on or off, no noises happen, no lights turn off or on either.

If the unit fails and then randomly decides to turn on as the car is warming up outside for a few minutes, it just turns on normally. It may come on in a few minutes, or it may never come on. My intuition is that if the sun cooks the car for a bit, then all functions normally.
--
------

Another thought:

When the ECC fails, bring it in the house (engine not running) and warm the box up. Bring it back to the car and see if it then works??? If so, it could be a solder problem.


https://www.ebay.com/itm/Z-2-98-00-VOLVO-S70-V70-98-04-VOLVO-C70-Automatic-Climate-Control-Unit-/182313203506
--
Keeping it running is better than buying new

Brought the ECC into the house after it sat in the car at 10 degrees Fahrenheit. After it warmed up in the oven for like a minute (not cooking, just warming it up quickly) I stuck it back in the car and it functioned.

So, I took apart the ECC and baked it at 385 for 9 minutes. The baking seems to have fixed the issue, so I suspect weak solder joints. HOWEVER!!! Since the buttons and vent direction and temperature controls are all plastic (even after removing the face of the unit) the high heat melted the buttons and knobs on the circuit board, effectively locking the unit at whatever settings they were set to when I put the ECC in the oven to resolder everything.

Mixed results. haha. Live and learn.

I ordered a used unit online.
--
------

Thanks for my morning chuckle! I needed that! I guess you won't need to re-solder.
--
Keeping it running is better than buying new

So the unit has no power when cold. That narrows things down quite a bit.

The large connector in the back, pin#1 is battery voltage. Pin # 6 is ground. (this is from a 1995 manual)

--
Keeping it running is better than buying new