Tracker 1.6 petrol engine . what should be the fan clutch r.p.m when fully engaged (30 deg. cel. ambient temp.)?
I measure a difference of 30 r.p.m between pump shaft & fan (using infra-red Tachometer).
is it normal?

I don't think it quite works that way - and ambient temp is of little relevance, engine temp is what matters - or to be more precise - the temperature of the air coming off the radiator.

According to the FSM for the Suzuki with the 1.6 engine (99 & later)...
- below 50*C the fan speed will be between 600~1300 rpm regardless of engine speed
- between 50~70*C the fan clutch will engage gradually
- above *70 the clutch will be fully engaged, causing the fan speed to increase in proportion to the engine rpms up to 4000 rpm.  Over 4000 rpm the fan speed will be 2800~3100 rpm.

So what was your engine temperature like and how fast was the engine turning?

When I checked, the fan temp. was above 70*C .
I saw the FSM, but it's not clear to me if at this situation (960 r.p.m & 70*C) a 30 r.p.m deviation between input shaft & fan is considered normal.

anyone?

...the fan temp. was above 70*C .  ... it's not clear to me if at ... (960 rpm & 70*C) a 30 rpm deviation between input shaft & fan is considered normal. 

The fan clutch uses a a viscous coupling, so there will always be some slip, just as with a (unlocked) torque converter in an auto trans.  30 out of 1000 rpm is minuscule.  I'd suggest that you need more data points. Try taking a measurement every 1000 rpm or so, if you can.  The fan clutch is a wearout item. If it's got over 100K, it's suspect. [My experience is Samurai and Volvo, but I think it still applies.]

Thanks Merlin,
I can check  this. but my problem is at idle (a/c not effective).
still, the FSM says: "above *70 the clutch will be fully engaged" does it mean no slip at all?
without comparing to a new unit, there is no way to tell the condition of the clutch.

I read somewhere that a fan clutch can be repaired by refilling, any information on this?

Thanks Merlin,
I can check  this. but my problem is at idle (a/c not effective).
still, the FSM says: "above *70 the clutch will be fully engaged" does it mean no slip at all?
without comparing to a new unit, there is no way to tell the condition of the clutch.

I read somewhere that a fan clutch can be repaired by refilling, any information on this?

I would not agree with that - the FSM provides enough detail to determine whether or not the fun clutch is functional without your having access to a new one for comparison purposes.

The fan clutch has two failure modes - it either slips more than it should - or it doesn't slip at all.

Start the engine and let it run for 30 seconds or so, before it is up to operating temperature (air temp off the radiator < 70*) measure the fan rpm - it should be between 600~1300 rpm - less rpm means, it's slipping more than it should, more rpm means it's not slipping enough.

Bring the engine up to operating temperature so that the air coming off the radiator is at 70* or more, bring the engine rpm up so that the fan pulley is turning at 4000 rpm or greater and measure the fan rpms - if the fan is between 2800~3100 rpm, the clutch is good - less rpm would indicate it is slipping more than it should, and of course more rpm would indicate insufficient slip.

As for repairing the clutch by refilling it - I've seen webpages that detail how it's done, and I know that at least one member of these forums says he has been able to do it successfully.

By the way - if - this ...

my problem is at idle (a/c not effective)

means that at idle, the a/c is not cooling properly, then you're looking in the wrong place.

The a/c condenser has it's own electric fan mounted in front of the condenser - it does not depend on the engine cooling fan to move air through it - if that fan is present and functional, check the condenser itself to make sure the fins are not blocked and then have the refrigerant system checked.

fordem, the condenser was flushed & drier replaced.
I checked the electric fan current and it was within spec. therefore, the next step was to check the fan clutch.

I drove downhill on an isolated road with a/c on at 40Km/hr with the gear in neutral for a few minutes.
the air coming out was 7*C (outside temp. 35*C).
then I stopped, engine idle. and after a few minutes air temp. climbed to 22*C.

I suspect that there is insufficient cooling for the a/c . the engine itself is not overheating.

I don't know if you're aware of this, but the FSM details a performance test for the a/c, which is somewhat different to your adhoc method.

If your worried about the manual fan going out I would hit a junk yard, find a fan that fit, build some quick mounts and just replace the manual fan and shroud with the electric kit instead.  No more worrying about if the clutch is working properly or not.