Thread: TD5 Aircon Thermistor

Originally Posted by shack

Hi Les,

I have no doubt you are right.

All I'll add to it is that I can't actually see any reason to have that setup on a 300tdi!

It's overly complex when you consider that the 300 has no ECU itself. So an old school 2 wire thermostat with variable positions has been replaced by an ECU, thermistor and 3 position temp control switch!

I've actually added an a thermostat override switch in my TD5 that keeps the pressure switch and still triggers the engine controller to run the AC and condenser fan.

I nearly went old school thermostat myself.

In fact, unless all the TD5 defenders I've used all had problems with either the AC ECU or the thermistor, I don't think they are well calibrated for the job. Much cooler if I use the override (probably uses more fuel and could also freeze the evaporator, but I don't care because it cools the car!)

But the wrecking yard thermistor will likely do the job.

Manual thermostat will do the same and I have replaced many that way, but in reality the thermister is far more reliable and a much easier fix.

My brother in law is visiting Africa in a week so I sent one to him from John Cradock which he will put in his luggage.

Originally Posted by LuckyLes

Manual thermostat will do the same and I have replaced many that way, but in reality the thermister is far more reliable and a much easier fix.

Why is a thermistor more reliable?

Genuine question as I don't know!

I guess we have had a thermostat or 2 die over the journey, but still curious.

Originally Posted by shack

Why is a thermistor more reliable?

Genuine question as I don't know!

I guess we have had a thermostat or 2 die over the journey, but still curious.

There are no contacts, or gas filled capillary to vibrate and crack. Electronics don't generate as much heat or use as much current to operate, and have a far lower failure rate.

Thanks for that explanation Les.

So I fitted the new OEM thermistor, replaced all O-rings and fitted a new Filter drier.

Ran a vacuum for 24 hours and confirmed no vacuum leaks.

Added 2 cans of refrigerant totaling 560 grams. Little bit short of full 600 grams. Going to top up with a third can when I get.

Noticed that I still have a strange sequence of compressor cutting in.

I turn the fan switch to position 1 but the compressor only clutches in when I turn the temperature to full.

When I turn the temp back down to position 1 the compressor still remains clutched in but does not cycle no matter how high I turn the fan switch.

It is pretty warm today so maybe the cab does not get cold enough.

The compressor only clicks off when I turn the fan and temperature both to off position.

Does anyone have the correct sequence of positions of both switches as to what is supposed to happen as the manual I have does not go into much detail.

Before I played with my system it was filled by my refrigeration team at work by feel and not by measuring but my probe in the air stream used to go down to minus 5'C but now reaches about zero degrees.

Originally Posted by CapeLandy

Noticed that I still have a strange sequence of compressor cutting in.

Before I go into the rest of the post, can you explain what you mean here?

Are you saying that the original problem was the funny operating of the switches?

The original problem was a squeaking fan bearing as to the reason I stripped everything. Was a very annoying sound.

I also thought at the same time I may as well strip everything to see why my compressor never cycles and suspected the thermistor, but during removal I damaged it so was not sure if it was already broken or just happened when I pulled it out the evap coil.

Now I am confused as to where the fault lies as the switches are fine but yet the compressor doesn't cycle. Could it be the little ECU box that's faulty ?