Volvo Maintenance Hints for 7xx/9xx - Bill Garland's Nuclear ...

system is integral with the control assembly. The relay usually isn't the problem, it is the solder
joints from the connector to PC board or PC board to relay pins. The relay is soldered to the
circuit board. When you remove the control panel you will see the metal enclosure for PC board.
[Response: James Abercrombie] The time delay for compressor start is integral in the
electronics of this board so there can be a failure of the circuit that stops the a/c compressor that
is not related to the solder connections, but this is very rare.
Applications: Solder board cracks can occur in the MCC, ACC and ECC heating/ventilation
control units and account for many of the system failures in these cars. If the heater works and
the a/c does not, take a look at the board.
Gaining Access to the CCU
PC Board. [Jay Simkin] To
access the printed circuit
board: (a) Gently straighten
the four twisted metal tabs,
which secure the shiny metal
inspection plate. (b) Once
the tabs are straight, lift the Broken Relay Solder Joint in Climate Control Unit
plate gently, using a small,
flat-blade screwdriver. (c)
Remove the four small
screws that secure the circuit
board (d) Do not touch the
ribbon connector: the board
can stay attached to the rest
of the CCU, while you repair
the printed circuit board. You will work on the underside of the board, where the mounting pins
for the devices at the top of the board, stick through the bottom surface of the board. (e) Find
the relay, a square, box-like device towards the edge of the circuit board (f) find the main
electrical connector - opposite where the ribbon connector is attached - which electrical
connector has 12 or 14 pins.
Re-Soldering the Control Unit PC Board.
Soldering Techniques. See the discussion and FAQ section under Circuits and Relays for
correct soldering techniques on boards.
[Responses: Philip/James Abercrombie] We had intermittant AC problems on our 94 940 turbo
that were cured by resoldering bad solder joints on the control board (behind the switches). As
usual you need a magnifying glass to see the bad solder. Ours looked OK, but had a dark circle
around the outside and black marks on the PC board from overheating. Re-soldered it and
saved $400 for a new one (there are no service parts for this unit.) Two key areas should be
examined closely: the connector joints and the relay (black box in center), especially the
compressor connections. The solder cracks at the points where the high current load is passed
through the PC board connections. [Tips: Patric Paul] The faulty solder spot is in the lower half,
a little to the left. Take your time and you will get it done. Don't overheat the circuit board while