Very hot 300TE with Low (& High??) electric fan cooling problem

Guys

I have been reading quite a few threads since my temp gauge went to 120+ in traffic a couple of days ago (ambient temp was 32C or about 95F). I tried to get the fans to come on by turning on the A/C but they refused, so I managed to lower it by turning down some side streets & getting some air through the radiator. (I added this to another thread but it occured to me that it might be better to post a new thread)

A/C works well & the belt driven fan clutch was renewed last year & seems to be working OK.

I've tried to do some tests and so far today (35C) I have had 1 fan come on high at about 95-100C (temp gauge) with the A/C on a short trip (right side looking at it from the front - your driver side - my passenger side).

Later I removed the Temp guage connector (which looked a bit beaten up) and the same fan came on high, but nothing from the other one.

When I bridged the plug I heard relays switching near the fusebox & near the A/C drier but no Low fan came on - in either of the fans.

I also tried bridging the each side of the Low fan resistor with 12v - but nothing happened either side. Though I may not have done this correctly?

Does this mean -
I have at least 1 fan that's dodgy;
I possibly have a Resistor that's stuffed;
Possible other problems...

Any help greatfully accepted.

PS - something else I was wondering is that when all of the R12 was replaced with R134a a few years back, how does this affect the psi readings from the A/C for the Low speed fan? Are they close enough?

Cheers

Stu