Cooling fan Ambiguity in Service Manual
The text of the 94 service manual says that:
The PCM will complete the ground path for the winding of the low speed fans ("Fan 1") when it sees Engine Temperature above 100C (212F), or when A/C is requested.
The A/C head pressure switch signals the PCM to turn ON the high speed fans ("Fan 2") relays when A/C pressure exceeds 210 psi (1448 kPa). "Fan 2" is also turned on when engine coolant temperature is above 108C (226F).
A page or two further on, the schematic shows the temperature-sensor and the A/C head pressure switch signalling the PCM.... but nowhere does it show anything about the A/C "on" switch which is what I would assume is meant by "when A/C is requested".
Is it, in fact, supposed to turn on the fans low-speed, when A/C is simply switched on???
In my particular situation, the fans appear to be coming on a few degrees late... about 104C on the dash gauge for low-speed, and about 114C for high speed. But they do not come on at all when the A/C is switched on (if the coolant is cool). Of course the A/C has leaked out a couple of years ago and is not working, so the head pressure will never be high enough to trigger the High fan-speed condition, but should the LOW speed come on anyway???? And if so, does this automatically mean a PCM problem??
Oh... and is it a reasonable assumption that replacing the temp sensor will solve the late fans? Or are there other possibilities for the late fans?
Coincidentally, a "low coolant" light comes on randomly, even though the coolant is right up and appears to be in good condition (glycol).