Refrigerator not working again

[Michael A. Terrell]

The only HVAC PC boards I've seen lately are all over eight years old, but the electronics industry, in general has moved from through hole to SMD to reduce assembly & component costs.

[The Daring Dufas]

Is there a particular brand you install? Me and GB have been installing Goodman and to tell the truth, I haven't bothered examining the darned circuit boards on the newer stuff we install. We have a buddy who's a Standard dealer and he charges a pant-load for his gear and $100/hr. I don't do anywhere near the volume of HVAC work you do so I'd have to defer to your experience. Hell, I was so tired when I got in today, I couldn't stand up for long and had to postpone fixing a leak on a very old Carrier heat pump. I know that sucker has no surface mount devices on its control board, it's older than the girls chase. 8-)

TDD

[The Daring Dufas]

It's hard to explain to people why a service costs so much when they pay a lawyer $150.00 for two sheets of paper without question. "What?! $150.00 !?? That paper only costs 4 cents!! What the hell?!!"

TDD

[The Daring Dufas]

I do more repair than new installation and there are scads of universal replacement controls at the supply houses that are a mix of technologies. The board may look very similar to the OEM board but will have parts moved around with surface mount devices peeking out from between the caps and relays. I'm getting to the point where I can't see too well anymore so the through the hole stuff is a lot easier for me to fix. I got tickled when somebody gave me a dead motherboard for a computer system and the only problem was a blown fuse and PPTC that were the size of a half grain of rice. 8-)

TDD

[Michael A. Terrell]

Keep your eyes open for a good stereo microscope. I preferred the B&L I had on my bench at Microdyne. Also, I liked the 'Multicore .015" rework solder. Surface mount isn't going away for small parts. A look at the Digikey or Mouser catalogs over the years will show that the availability of leaded parts is dropping every year. The same, with components using real solder without tin whisker problems.

[aemeijers]

And nobody sees a basic problem with design philosophy here? Control circuits for an HVAC system need to be closer to an anvil, than to avionics, to meet design lifespan if nothing else. And they need to be field-repairable. If it can't be at component level, there needs to be an industry standard for board interfaces and mounting, so that the unit cost of boards can be low enough to repair at board-swap level. (Yeah, I know, there are always plenty of standards to choose from.)

I know nothing about HVAC beyond 'no worky -> pick up phone'. But I have worked in computers at the field support interface for 20-some years, and have run into similar issues. Engineers in that field violate KISS principle on a regular basis as well, and component level repair vanished years ago.

[ATP]

EMI split units are notorious for bad electronics and quirky on again, off again failure modes.

[Stormin Mormon]

Household full size refrigerators. Not relatives, and I've got very few concubines, or wives. Couldn't have any fewer, actually. 1/4 plus, or 1/3 HP. Did a 10k BTU AC compressor a couple weeks ago. I suggested to get another whole unit from Walmart, but he aparently liked this one.

Largest I've done has been a 2 HP for a walk in cooler.

[Steve]

I install the Rheem "Prestege" -JEZ series almost exclusively for both A/C and heat pump condensers. My entry level systems use a 13SEER condenser, but with the correct coil and air handler/furnace combination, the system is rated 14SEER or better. My "premium" systems are 16+SEER, 2 stage, serial controlled systems. FWIW, I have not installed an R22 system in 5 years, only R410a.

[Michael A. Terrell]

Sigh. It would be great if HVAC electronics were built to Avionics standards. For one thing, Avionics is 100% exempt from lead free solder. For another, equipment design is always at the 'Mission Critical' level. Avionics are built for long life, with little or no maintenance. It is usually there for the life of the aircraft, unless that series undergoes an across the board redesign. Of course, it would double or triple the retail costs of the controller.

One thing I've seen in a lot of failed programmable thermostats is that they use slide switches that are installed before the boards are cleaned. Then the board cleaner washes out all of the contact lubricant.

How do you propose to do that? If you make an interface to handle any possibility, you add a lot of costs. Surface Mount is actually easier to repair, if you know what you are doing and less susceptible to board damage if you know how to solder.

If you are a hack at electronics, then all bets are off.

Strange, because I still repair some motherboards. A lot of failures are bad low ESR electrolytics, or cracked ROHS solder joints. Until I ended up 100% disabled, I repaired 68340 based embedded controllers at the Microdyne factory. I also tested and repaired all of the boards in our dual receiver DSP based RCB-2000 telemetry products.

Contrary to popular belief, having schematics isn't always a help. OTOH, having the datasheets for the ICs is.

A lot of techs have no idea why some things are done. For instance, I see people bitch about 'Those morons put the electrolytics too damn close to the CPU! Why can't the bastards put them on a corner of the motherboard, away from the heat?" Well, they carry a high ripple current, so they are self heating. The CPU us a high current, low voltage device, so the regulator has to be close to the load. Long traces would radiate a lot of EMI. A lot of power would be wasted heating the copper traces, and the inductance would screw up the regulation.

Buy a ESR meter and test the electrolytics on those boards. A little ripple can cause all kinds of problems. 30 years ago I was doing bulk repairs on 'Linear' brand garage door opener controls. Every one of them needed new electrolytics. They were always mounted in hot locations, and powered 24/7. Similar to the environment in HVAC systems.

One thing that makes it hard to repair those boards is that the techs don't use logical troubleshooting methods. They use hunches, or just shotgun a board till it starts working, or they destroy it with sloppy soldering or installing parts wrong.

[The Daring Dufas]

I just fixed a ViewSonic LCD monitor for a customer's POS system and it turned out to be a common problem with a 16 volt 1000 uf cap on the power supply board. Looking closely at the board, I saw another pair of holes for a parallel electrolytic. I soldered in two 470 uf

35 volt caps in place of the original single since they fit the space. The customer has had damage to various electronic gear due to power surges and I've had to replace the KSU for his phone system when the POTS line ports were blown. I don't understand why designers will take such a cheap route when they know there's a possibility for a piece of equipment to be subjected to aberrant voltages in the power source for many of the end users. I remember how the original IBM PC's were built like tanks and you paid a price for that robustness but now so much of the electronics we get these days is a commodity item and the penny pinching paper pushers (hey, I made a rhyme) want engineers to spit out products as cheaply as possible. It's amazing how just a few more dollars spent on an electrical/electronic item will extend the life of that product.

TDD

[The Daring Dufas]

I think the largest freezer I ever worked on belonged to a bakery and it was the size of a basketball court. Forklift doors and 20' high pallet racks were in that darn thing. It was a lot of fun getting way up in the air to work on the multiple evaporators. Believe it or not, it's easier to work on than a little freezer, you can get to every part.

TDD

[The Daring Dufas]

Me and my homey works fo mostly po folks dat doan has a lots O money. We found a new 3 ton R22 heat pump condensing unit at Johnstone this Spring to replace an old unit for a customer who's air handler and evaporator were in good shape. This Summer, we replaced an old R22 system for a friend with a new R410a system and we darn near toasted to death. It was in the middle of the hottest Summer we've had in a long time with temps in the 100°+ range for many days without end. I didn't have to pee for

8 hours, it all came out of thousands of tiny holes in my skin. 8-)

TDD

[Steve]

Welcome to my world :-)

[Michael A. Terrell]

Were they low ESR 105° C or 125° C parts?

Add some Endeco protection to the incoming lines. The do an amazing job. I have nothing to do with that company, other than the dfact that some freinds of mine bought their old factory and moved into it a few months ago.

It's commony reffered to as 'The race to the bottom', since people are price driven.

[The Daring Dufas]

They were probably 105° standard aluminum electrolytic consumer grade. I just wanted to install a higher voltage rated part.

On the AT&T termination, there are usually gas tube arresters in commercial buildings. There are two different types commonly out in the field. I often add an additional protector with a solid state unit in front of the phone systems. The carrier will accept either the gas tube or Silicon Avalanche Hybrid modules. If I have to, I add fuse modules in place of shorting clips on the 66 blocks for systems that get hit often. It's not unusual for me to have to argue with the phone company that the a module is blown at their central office. They have to send a tech out to check it on my end. I once called customer service to complain about a longitudinal imbalance on my line because a sewer crew had hit the buried cable to my building and the fools just wrapped tape around it and tossed it back in the trench. The CSR said "Sir, we can't get involved in your personal affairs." I said "You don't understand, my phone line was damaged by a BACKHOE, that's a big digging machine, not a woman."

Heck, I'd like to have more than one quality choice. 8-)

TDD

[Michael A. Terrell]

You have to be careful if they are low ESR parts. Higher voltage caps have a higher ESR.

Endeco makes the plug in protectors, as well as wall mount. I think they also made a 66 block with built in protection back in the late '80s.

I had a radio station with problems with live call in. On line was over 20 dB lower in level, and they tried to tell me that was normal. The switching center was directly across the street. Less than 150 feet of wire, and they expeccted me to fall for their BS. It turned out to be a bad card in their switchgear.

I had a direct hit on a building. It arced to a telephone cable that ran two miles to the main road. It blew out the SLIC at that point, and vaporized most of the copper in that pair, all the way to the CO, where it took out another card.

No kidding! :(

[Stormin Mormon]

New product line: Full body Depends for HVAC techs.

[Stormin Mormon]

Yes, I can imagine that being easier to work on. One of my regular gas and go customers has a walk in refrigerator. Naturally, it leaks at the nut for the TXV. The folks who designed the cooler allowed about two inches from the end of the evap to the wall. I get to tighten the nut while standing on crates of soda pop, and balancing a miror, wrench, minimag, and trying to not fall.

[Michael A. Terrell]

If the job was easy, anyone could do it! ;-)

I would have traded you jobs back in the '70s when I had to stand inside TV transmitter in full operation to adjust the interstage coupling. Nothing like standing on a 3 KV power supply with a fault current in excess of 10KA while bending the wire loops with a piece of nylon rod. :(