Vehicle is 1991 740 Wagon AT non-turbo. The weather in VA is just warm
enough that we turned on AC last week for the first time in many months.
AC was fine last summer but no cool air now. With vehicle idling, the
AC clutch kicks in for 3-5 seconds, then stays off for 10-15
seconds. Also the electric cooling fan in front of the radiator is
not operating. I bypassed the radiator temp switch and confirmed that
the cooling fan runs fine. I thought the cooling fan was supposed to
run all the time when AC is turned on ? Thats what I remember but
it is not happening now.

I am suspicious that repairs last fall at a local shop may have
affected the AC and we never noticed until now. The AC was
fine before the shop replaced items like motor mounts, heater
control valve, timing belt, drive belts, shifter quadrant illumination
bulb. These are all areas where wiring or vacuum hoses could have been
disturbed. So far a visual check has revealed nothing disconnected
but it could be hidden.

Questions:

1. Where can I find a wiring or system diagram for the AC on
this vehicle ? My Haynes manual only covers through 1989 and
the wiring diagram is incorrect for 1991.

2. Should radiatpr electric cooling fan run all the time when AC is on ?

3. Does the AC ECC unit have a diagnostic light ? The AC control
panel on our car has a button (out for AC on) and a
button for Recirculate but no light. Where is the AC ECC ?

Thanks,

Mike

First, your system is low on refrigerant; that's why the compressor cycles.
Fix that and then worry about the fan, if necessary.
--
Jim McDonald

I agree with Jim McDonald's diagnosis....compressor is cycling too fast because you are low on A/C refrigerant--the low pressure switch cuts out the compressor so it is not damaged by lack of lubrication ....same symptom I had two years ago....I discovered a leaking A/C condenser....carefully examine all A/C connections, lines, hoses, etc. and look for oil spots.....

If your '91 740 wagon is like my '91 740 sedan, the electric fan in front of the A/C condenser does not run continuously when the A/C is on. The fan is activated by the coolant temperature switch in the radiator (top left side of the radiator as you face the car). To test the electric fan, disconnect the two leads to the switch and touch them together....fan should come on. If it does not, switch, relay, or fan is bad.

The electric fan in my car rarely comes on....I live in NC, so it gets plenty hot here.

Hope this helps some,
Jim Nau
'91 740, 130K
--
Jim Nau