heat pump problem

[Ralph Mowery]

The control circuit is 24 V AC. The block diagram shows a relay contact or two in series with the motor contactor for the compressor.

I had forgotten I had the diagram from last year when it acted up. Just cutting it off and back on cleared the problem, so I did not go into it last year. I had so much going on the day it quit on me this year, my mind was on other things.

The LED has 3 or 4 flash rates to indicate a couple of problems. It flashes normal. It may be as simple as a bad connectiion of dirt on one of the relay contacts.

The thing quits so infrequent it is difficult to trace when other things are going on.

Often in simple circuits (and more complicated ones) a product will have several known faults that hapen 90 % or more of the time. I just though someone may have ran into it before.

[gfretwell]

You are right, mass production means mass failures if there is a flaw in the process. In my biz, every machine usually only had a few things that went wrong. If you could identify the flaw and come up with a fix in the process, there was money to be had.

[Bod F]

Check for loose or corroded terminal connections.

[TimR]

The people who work for me fall into couple of groups on troubleshooting.

One is in the camp of: It's a <brand XXX> <model 123> so it's always a faulty output relay. They're right a lot of the time and that reinforces the approach. When it's wrong they're lost.

Another is: Gather all the data, check everything, avoid a diagnosis until the last moment. These guys are slow but get it right. I've maybe got one like that.

The most common though is to make the diagnosis too soon and then exclude all data that doesn't confirm it. I try to keep these guys away from expensive equipment but there's no way to fix their approach. It's not that they ignore conflicting data, they can't actually see it.

[Ralph Mowery]

I like to think that I fall in the middle of that.

When working on equipment, about 90% of the time it will be the same part that fails. For example at work there was a piece of equipment that had a relay in it that often failed. It just plugged in. Instead of taking time to think about it, I would put in a new relay. Takes about 10 seconds. If that failed to fix the problem, then out comes the test equipment and circuit diagrams to do the trouble shooting.

[Clare Snyder]

There's one other type, and they are the most irritating. The ones that got lucky once and doing "X" fixed it -so that's always the problem - - - Can't tell them anything - can't teach them anything - particularly when what they decided was the solution to the problem was "replace everything" - with a different part.

[Clare Snyder]

I do similar - but usually I "test" the relay (or whatever) to either prove it IS the problem or it IS NOT the problem. This is because I don't always have the replacement part available, and in most cases if I get the part and it is NOT the problem it is not returnable - and I'm stuck with it. If IDO have a "Known Good" part to swap in, it IS (generally) the quickest way to prove the fault.

[Ralph Mowery]

If I had to buy a part, I would try to make sure it really was bad. Where I worked, we had thousnds of spare parts as the plant needed to run 24 hours a day, nonstop. Usualy had one or more replacements for most everything. Those were small realys and I would usually put one in my pocket before I left the shop as it was in another building. I also carried some test equipment just in the rare case it was not that part. There was another part that was known to fail so took one of those with me, but as it took about 20 minuits to change it out, I would run a few tests to determin if it was the problem.

I did have a Toyota that started running rough. As I am not a very good car mechanic, I threw a few logical inexpensive parts at it. Plugs, wires and coil. The hint page on Autozone pointed to a mass air flow sensor, but it was around $ 500. Took it to the Toyota dealer thinking they could test it. Two weeks or more later they finally decided it was the sensor and put in a new one. Not sure what kind of mechanic they had, but did not seem to be much of one.

Then there are the ones that do not have a clue and do not seem to know what to do, so they just change parts blindly.

[gfretwell]

Goes a lot faster if you know what to test first. The best test is to plug in the good one you have in your pocket. ;-) I have worked on all sorts of machines and some you really needed to diagnose (like a CPU with 1000 cards in it or a check sorter with

10,000 moving parts). Since the 90s, just replacing the bad part based on a few symptoms, is not an unreasonable approach. When I left in 1996, IBM pretty much said take a scope with you, take two, we don't need them anymore. (along with a trunk full of other test equipment). They didn't need me either. Any dweeb can work on a box with a half dozen FRUs, functionally packaged.

[Clare Snyder]

The MAF on the 22RE and 4MGE as well as many others was actually REALLY easy to test with an ohm-meter and your finger.(I was Toyota service manager for 10 years from '79 to '89 and toyota tech back in '72

[trader_4]

The onboard diagnostics and code setting could be better too. I posted the other thread about the BMW X5 having issues and then suddenly not running at all. As I said there, it was the intake plumbing coming apart just after the MAF. I spotted it visually. But before resetting all the codes, I decided to read them out just to see what was set. I made a bet with myself that MAF problem would not be one of them. I was right. It had lean codes set, misfire set, idle air valve not working...... No MAF codes.

You'd think with little air moving through the MAF it would say something like MAF output low or inconsistent. Or MAF output implausible. Those Germans like implausible. For example if the brake light sensor is bad, it will say Implausible - Simultaneous brake and throttle. But you have the engine running, albeit poorly, at 3000 RPMs with most of the air not registering through the MAF, and no MAF codes.