Alarm 48 Thermo King Spectrum

[george106]

The problem is that the unit very often shuts down with alarm code 48 when it runs in low speed.
Engine rpm ok.
Belts clutch ok
Alternator ok
I also check the W wire from the alternator to the micro (I have about 8volt ac to the alternator and the micro)
My costumer has 2 spectrum units that he buy the same day (about 4 years now) and they were new
Any suggestions?

[cadwaladr]

replace the belts code 48 is belts slipping or clutch inspect the belts sometimes they look ok but on closer inspection they are not how many hours has it done since the last belt change

[SteinarN]

Is it a SL Spectrum?

On a few units I had to increase the low speed by 100-200 rpm to get rid of A 48 on low speed. That was on SL Spectrum units with factory low speed at 1400 rpm.

[george106]

It`s not for belt slipping or clutch for sure.
Yes it is a SL Spectrum. I increase the low speed to 1500 rpm with no luck. Maybe i increase it more to 1600 and i tell you the result.

[clivemtk]

altenator brushes or faulty diodes in altenator

[george106]

The unit is tested with new altenator with the same result.

[DTKServices]

Does the unit shut down every time it goes into low speed?

If So How long before it shuts down?

If not it there good continuity on the w wire at the Alt and at the micro? (Not voltage or voltage drop)

If you by pass the wire harness, and run a separate (W) wire will it shut still down?

If you can eliminate the wiring/pin connections, I'd look at micro/programming or that the clutch isn't in fact slipping..

[abbsnowman]

We don't have these units over here so I have no manual but I have to start with first things first, What tells the micro that belts are slipping? (alt voltage, oil pressure, head pressure?????) What does the book say?

[george106]

The unit doesn`t shut down every time it goes to low speed.
No voltage drop to the W wire at the alt and the micro.
Yes i test it with a separate wire from the alt to the micro.
The revision of the eeprom is 1022
The best of all is that the units shuts down with alarm 48 from new (about 4 years)

[SteinarN]

We don't have these units over here so I have no manual but I have to start with first things first, What tells the micro that belts are slipping? (alt voltage, oil pressure, head pressure?????) What does the book say?

Hi abbs :)

It's the Hz at the W terminal at the alternator. This Hz is proportional with the alternator rpm and must be between 400 and 600 Hz I have been told. As this alternator has 6 poles, 400 and 600Hz is corresponding to 4000 and 6000rpm. There is no difference in the required Hz in low and high speed. Therefore the belts can actually slip a lot in high speed before the unit shuts down on A48.

[george106]

Is there a way to measure the Hz at the W terminal at the alternator?
If the Hz is below 400 what part of the alternator i have to replace?
Thanks a lot i think that we are close to the solution.

[SteinarN]

I good multimeter should be able to measure it. The signal does however consist of a lot of electrical noise. This can lead to an unstable measurment or impossible to measure at all with a cheap multimeter.

[SteinarN]

One other method is to measure the alternator rpm directly with an optical tachometer. The rpm in low speed shall be no less than 4.000 rpm.

[abbsnowman]

Probably not in this case but I have seen Carrier truck units do this because of a worn pulley on alt.
Thanks for the info Steiner. Good to see ya here!:D

[clivemtk]

hi george106 do you still have fault with unit

[george106]

Hi all
I took an alternator from a unit of my customer to make some measures
I let you know if I have news

[clivemtk]

hi george106 when you tried different altenator did you use orginal pulley i had same problem a pulley for a unit30 wasabout 90mm a pulley for a 50 unit about 95-100mm this alters your hz measurments and gives code48

[MRW]

remove flywheel sensor clean and refit,all the way in then back off 1/2 turn,the code 48 logic looks at the hz from the flywheel sensor against the hz from the w on the alternator,they alter proportionatly as the engine speed changes

[clivemtk]

hi george 106 have you fixed unit yet

[Latte]

silly question i know, but why does the measurement for belts slippind come off the Hz reading. What does it protect and doesnt all the other shutdown alarms cover all the other problems so 48 isnt needed. the SR's cover charging so it the belt snapped that would alarm. if the compressor belts snapped the fans would stop, causing pressure faults. Code 48 has always been a problem why actually have it

Regards

Latte

[abbsnowman]

You pose a realy good question. I will try to find some info on this because I doubt that it's there to irritate us. Anybody else willing to read up on this?

[Latte]

I doubt that it's there to irritate us.

Guess what IT DOES !!!!!!!!!!!!!!:D

[The Fox]

code 48 exists to protect against a problem in the drive chain. If for example you had a problem with the comp. starting to seize the engine would on a 50 unit continue to turn but the clutch would be in danger of burning, this being the case the logic in the controller would notice that the differance in the htz output from the alt. and the engine rpm and shut the unit down.bascally its a safty feature,,,,,