Bosch
C3 / C4
ProtectCondenser coil sensor seating
T3 reads implausible vs T4 (T3 < T4 − 3°F for 10 min).
Walk C3 / C4 in Diagnose
Sign in for the next measurement
First check
1 Which sensor is this code?
On Bosch BOVA 2.0 C3 / C4 is a specific thermistor — indoor return/pipe, outdoor coil, discharge, or ambient. Unplug that sensor and ohm it vs the OEM temperature/resistance chart. T3 on the outdoor coil U-bend per the diagram, not hanging in air.
Expect: Ohms move with temperature. Not open, not shorted.
The rest of the walkthrough is Diagnose.
On the plates
- T3 on the outdoor coil U-bend per the diagram, not hanging in air.
- T3/T4 10K ohms. 18 SEER has one T3; some 15/20 SEER have T3 and T3L.