heat pump problem

snipped-for-privacy@snyder.on.ca says...

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.
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On Sun, 1 Dec 2019 15:24:46 -0500, Ralph Mowery

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
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On Sunday, December 1, 2019 at 3:24:57 PM UTC-5, Ralph Mowery wrote:

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.
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wrote:

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.
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wrote:

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.
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On 11/29/2019 6:56 PM, Ralph Mowery wrote:

Check for loose or corroded terminal connections.
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On Friday, November 29, 2019 at 4:50:14 PM UTC-5, Ralph Mowery wrote:

Shouldn't even need a circuit diagram to trace the wiring. Look for the color of wires that drive the contactor outside and look for them in the cable coming from it to the air handler control board. Also the terminals should be marked with something that you can decipher by looking at it. If there is 24v there when it won't run, then wiring is the problem, otherwise look at what's at the W terminal from the thermostat.
It must be in that as the relay did not have any voltage across

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On Fri, 29 Nov 2019 15:23:26 -0500, snipped-for-privacy@aol.com wrote:

+1
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On Fri, 29 Nov 2019 12:00:59 -0500, Ralph Mowery

next time it doesn't run check for voltage out at the controller instead of voltage in at the contactor
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On Friday, November 29, 2019 at 11:27:29 AM UTC-5, snipped-for-privacy@aol.com wrote:

Furnace is as I described. The thermostat just calls for heat on the W wire (or wires if it's two stage), the furnace does the rest, ie turns the blower on after the furnace has fired for a minute or so. Old furnaces used to use a temp switch in the plenum to activate the blower. New ones just use a time delay on the controller board.
An interesting side note with two stage furnaces. They can generally be set up two ways. One is really the right and best way, which is to use two heat call wires, one for each stage. The other way is to just use one wire and set it up so the control board makes the call based on how long the furnace runs. So, it starts at low stage, then if it's still running after ~ 8 mins or so, it goes to high. Obviously that's far from ideal. If you need a bigger increase in temp, you have to wait 8 mins for it to kick up. And it also might kick up and then shut off in a just another short period, if the temp was almost where it needed to be.
The thermostat knows what the req increase is and can invoke high stage at the beginning. But it takes an extra wire, that many installs probably don't have. It also takes a two stage thermostat. I'd also bet that a lot of furnaces are installed using the inferior method anyway, because the installers are half-assed, don't want to change to a two stage thermostat, etc.
I do know you can run most heat only

Bingo.
He is definitely in the situation where poking around

I agree, I'd do more investigating, starting with what the voltages are at the inputs to the unit and at the activation terminal going to the heat pump.
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heat pumps have a lot of crazy modes for defrost etc.
does yours also have resistance coils heating?
maybe it was in another mode?
m
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