Rheem 97MDV060 Series Installation Instructions Manual page 53

The adjustment wheel is shipped from the factory in
the nominal position (noted as position A on the
Wheel). The wheel can be adjusted four full revolu-
tions (or 64 clicks) clockwise to increase manifold
pressure or four revolutions (or 64 clicks) counter-
clockwise to decrease the manifold pressure. Each
click is a very minimal adjustment and several clicks
may be required to adjust the manifold pressure to the
necessary 3.5"wc (natural gas) or 10.0"wc (LP) for
high fire. Further, it is recommended to wait a mini-
mum of ten seconds after an adjustment to verify the
new manifold pressure. Therefore, the installer must
wait at least 10 seconds for each click before adjust-
ing to the next click.
Use the marking on the wheel as a guide. The adjust-
ment wheel will not stop rotating when the valve's out-
let pressure reaches its maximum or minimum value.
Instead, the wheel can be rotated further but no fur-
ther adjustment to the outlet pressure will be made.
Once the maximum adjustment (high or low) is
reached, the wheel can be turned in the opposite di-
rection and this will cause the pressure to also move
in the opposite direction. The first click in the opposite
direction will cause a pressure change in the opposite
direction even if the maximum adjustment in the origi-
nal direction has been exceeded by several clicks.
If power to the furnace (and therefore the gas valve)
has been interrupted and the adjustment wheel turned
while power is off, the outlet pressure of the valve will
not be adjusted and will remain the same and will be
re-assigned to the new wheel selection. For example;
if the valve outlet pressure is at 3.5" with the adjust-
ment wheel at selection "A" and power to the unit is
turned off, and the wheel adjusted to positon "E"
(while power to the unit is still off), and power is re-
stored once again, the pressure will remain at 3.5" but
the wheel will now be set to position "E".
9. Check manifold gas pressure.
10. Repeat steps 8 and 9 if needed.
11. Remove jumper across R and W1 to remove heat call
and allow blower to finish off delay.
12. Disconnect 115 volt power to furnace.
13. Turn gas off at manual gas valve and remove the
manifold pressure tap and replace with outlet pressure
tap plug.
14. Set dip SW11 to the OFF position.
15. Reconnect all thermostat connections.
16. Turn on the gas supply and check for leaks using an
approved leak detector. Do NOT use a flame of any
kind to check for leaks. Repair any leaks and repeat.
ADJUST MANIFOLD PRESSURE AT
MINIMUM FIRING RATE
1. With the gas to the unit shut off at the manual gas
valve, remove the outlet (outlet/manifold) pressure tap
plug in the gas valve. See Figure 39.
2. Install field supplied pressure tap to the outlet/manifold
tap in place of the plug. Connect the positive pressure
hose from a manometer to the pressure tap.
3. Set dip SW10 to the ON position and dipswitch SW11
to the OFF position (this will force unit to operate at
Minimum Firing Rate (40%) only)
4. Remove all thermostat connections to the IFC and
jumper R to W1.
5. Turn gas manual shutoff valve to ON position.
6. Turn on furnace power supply.
7. After ignition, allow furnace to operate and complete
the pressure switch calibration before checking mini -
Note: The manifold gas pressure to be:
mum firing rate outlet/manifold pressure.
A. 0.56" w.c. (±.1) for natural gas.
B. 1.60" w.c. (±.2) for LP gas.
8. To adjust the outlet/manifold pressure, insert a small
slotted screwdriver into the opening at the top of the
valve (see Figure 41.)
The adjustment wheel is shipped from the factory in
the nominal position (noted as position A on the
Wheel). The wheel can be adjusted four full revolu-
tions (or 64 clicks) clockwise to increase manifold
pressure or four revolutions (or 64 clicks) counter-
clockwise to decrease the manifold pressure. Each
click is a very minimal adjustment and several clicks
may be required to adjust the manifold pressure to the
necessary 0.56"wc (natural gas) or 1.60"wc (LP) for
low fire. Further, it is recommended to wait a minimum
of ten seconds after an adjustment to verify the new
manifold pressure. Therefore, the installer must wait at
least 10 seconds for each click before adjusting to the
next click.
Use the marking on the wheel as a guide. The adjust-
ment wheel will not stop rotating when the valve's out-
let pressure reaches its maximum or minimum value.
Instead, the wheel can be rotated further but no fur-
ther adjustment to the outlet pressure will be made.
Once the maximum adjustment (high or low) is
reached, the wheel can be turned in the opposite di-
rection and this will cause the pressure to also move
in the opposite direction. The first click in the opposite
direction will cause a pressure change in the opposite
direction even if the maximum adjustment in the origi-
nal direction has been exceeded by several clicks.
If power to the furnace (and therefore the gas valve)
has been interrupted and the adjustment wheel turned
while power is off, the outlet pressure of the valve will
not be adjusted and will remain the same and will be
re-assigned to the new wheel selection. For example;
if the valve outlet pressure is at 3.5" with the adjust-
ment wheel at selection "A" and power to the unit is
turned off, and the wheel adjusted to positon "E"
(while power to the unit is still off), and power is re-
stored once again, the pressure will remain at 3.5" but
the wheel will now be set to position "E".
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