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Climate Control Unit (CCU) - Capacitor Replacement

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Introduction
The Climate Control Unit (CCU) of the NSX suffers from aging capacitors the same way as many other ECUs in the vehicle. It's often the first ECU experiencing problems. It typically takes about 25 years to manifest itself but high temperature and humidity can cause issues to appear even earlier.
A capacitor replacement should be performed as a precautionary measure even if no problems have been observed yet.

Diagnostic
Typical symptoms are a cabin fan that runs on highest setting only, a unit that won't switch on or other strange behavior. A self-test might show errors that can't be verified. If these or similar issues are observed and the unit is older than 20 years, it's safe to assume that capacitors have leaked and the PCB has taken damage - a simple replacement of the capacitors is no longer sufficient at this point.

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Acid leakage destroying PCB traces


Preparation
The Climate Control Unit consist of two PCBs - one main PCB and a smaller display PCB. The display PCB is typically unaffected and the two can be separated by means of four screws at the side and two multi-pin connectors.

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separated but not detached yet

Damage is not easily detected by the untrained eye but becomes obvious once the capacitors are removed. The unit below was already malfunctioning even though the owner stated that he didn't see any trouble upon a first look at the PCB.

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The above mentioned board

Before de-soldering all capacitors it's advised to make a list of the location, size, voltage and value of each one on the board. The CCU main board was produced in several revisions that can be identified by it's color but the number and location of the capacitors stayed the same across all build years.

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click to enlarge

To improve robustness it's advised to use capacitors with a higher temperature rating than those originally installed. The factory rating states a lifetime of 1.000 hours at 85 C. An improved replacement should be rated 1.000 h at 105 C or more. Note that increasing both the maximum temperature as well as the lifetime rating results in an improvement.
To avoid any damage due to leakage, dry (Aluminum Polymer) capacitors can be used as a replacement. Their price is significantly higher but guaranteed to be safe for the PCB even in case of failure. This is the corresponding DigiKey purchase list (note that one capacitor was not available as Aluminum Polymer and therefore replaced with a 10,000 h @ 125 C electrolyte type).

Repair
All electrolyte capacitors on the board need to be removed. The best way is to use a professional de-soldering gun but de-solder wick or a manual de-soldering tool can be used, too. The soldering iron should be electronically controlled as a fixed wattage type can have trouble with larger copper areas.
Areas affected by acid from the capacitors will either turn the PCB's green silk screen darker or lighter in color. All those areas need to be fully stripped of silk screen down to the copper layer and all traces of acid cleaned off. If areas underneath other parts are affected, these parts need to be removed, too (they can be potentially damaged as well, although in case of the CCU this seems to be a rare case).

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Traces darkened by acid

Use a small wire brush, a small screwdriver or other small scrubbing tools to remove the silk screen paint and carefully clean the area. Potential cleaning substances are a mixture of baking powder with water (to neutralize the acid) followed by rubbing alcohol or Isopropanol.

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A cleaned area

To strengthen the remaining copper, open areas should be covered in solder. This has the added advantage of indicating all areas where the copper is completely gone and are in need of a repair using jumper wires.

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Traces covered in solder (note eaten traces)

Traces that have been completely eaten by the acid can be repaired in two ways: Laying bare, 0.5 mm copper wire across where the trace used to be (often limited by the potential connecting points) or by running a patch wire across the bottom of the PCB, directly connecting the necessary components at their pins.

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New capacitors installed


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Installed jumper wires


Before re-installing the PCB into the CCU housing, it needs its conformal (protection) coating restored. All areas affected by de-soldering or mechanical cleaning need to be painted with a PCB protection to be robust against humidity or other corrosive influence in the vehicle.
It's possible to either spray the whole PCB (make sure to mask-off the connectors) or repair individual areas by means of a small brush. One suitable product is Plastik 70 from Kontaktchemie.

After installation into the car, run the self test routine to ensure all CCU functions are back to normal.

Updated 02-01-2021 at 10:04 AM by Heineken

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