Fabio421

I have a burnt diode on my HVAC control unit. This is in my 84. My plan was to de-solder the diode and then get the #'s off of it and match it up with a new one. Well.................things are never that easy. While de-soldering it, the ceramic casing shattered into a hundred tiny pieces. None of which are big enough to read the #'s from. So, does anyone have a write up or something that will help me with this. I will post a pic of the HVAC circuit board and show exactly which diode is in question in case that helps.

Thanks in advance for your help.

Landseer

My interior is pretty much out, with console set in place. So, my HVAC unit is probably accessible with about 10 minutes work.

Show the pictures and I'll try to identify it for you from mine,. assuming the answer doesn't show-up in the meantime from some deep archive somewhere.

Fabio421

Ok. Heres the picture. Thanks.

Landseer

Trying to get the case open now. Order of disassembly? Does the faceplate need to come off first? No clearly not, yours is still on....

Landseer

Looks like it says 1N. Can't make-out other marks yet.

Slightly smaller dia than others on the board.

Will get pictures up before 7:30 so you can see for yourself. Tried to use digital to get some enhancement, but hard to shoot in that tight space with autofocus.

Radio Shack sells 1N4003 micromini's, i bought some for the hatch motor repair attempt. Probably cost less than $1.

The orientation you show in the diagram in yellow is correct, with silver line opposite of the nearest diode.

the flyin' scotsman

fabio...........is the burnt diode similar to the 2 diodes next to it? can you read them?

Landseer

Pictures of the diode we are trying to identify:

the flyin' scotsman

nice pics but??? I looked at the wiring diagrams for the 84 but it doesn't show component values.

Chris is your soldering skills are of such you could remove, re-picture and re-attach?

Fabio421

It looks like it says 1N4???? on your picture. I looked up "1N4 Diode" w/ google and I guess there are lots of possibilities. Can you tell if the numerals wrap all the way around to the other side? If so, can you see any #'s there? If not, how many numbers does it appear would fit in the space available? I really appreciate your help with this.

As you can see in the picture now, its a little different. Maybe Jim Bailey or Wally might know and be able to add to the discussion tomorrow.

Landseer

Ummmm. I can do it if its absolutely needed. Just got done reinstalling the unit in the dash, though.

Can't read the backside of it. Starts 1N4.... Like the others. Can make out 1N4007 on the larger ones.

Maybe somebody knows the answer.

Who can give us a quick primer on diode sizing?

Fabio421

Very interesting. Lets hope so. I look into that.

Thanks

Landseer

I tried everything but removing it. Magnifying glass.

We played with 6 or 7 photos, zooming way in, but could't pickup any more numbers. I think the number is against the board.

Sorry, fell short so far on this.

Landseer

I think the lower mark in the first picture is the mfctr symbol.

the flyin' scotsman

The Vishay site list 1N4 diodes as 'Power Zener Diodes'.

IIRC Z diodes are used to control a certain voltage; once the voltage is exceeded the diode opens and current is then grounded.

Given this we best be very careful in gaining the correct info............dont want nothing getting to hot a sparking a fire!!!

dr bob

These are straight basic diodes, with 1 amp maximum forward current. They are used as isolation and 'logic' diodes in this application. A common 1N4001 will do the job nicely. It's rated at a hefty 100 peak inverse voltage, which should be plenty.

I guess I'd bein terested in what caused the old one to fail. The only thing that draws any significant current in that system is the AC compressor clutch coil, and that's got a relay doing the switching.