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Makeit go Right
27-01-2007, 09:28 PM
A Midea 3.5kW split system (heatpump 407c), which had been installed almost 1-year ago, was playing up on Friday. The warning lights implied “over current protection” and after 4x auto-resets, it tripped out. The customer said that he had been overcoming this by switching the system off at the isolator, and then switching back on “and that seemed to clear it”. Well, shutting off and switching back on does reboot the system’s protection controls but it does not deal with the underlying cause. And the problem has been repeating. Looking around the system, the condenser was clear of debris and no sign at all of frosting up (you could see right through the fins). Outside temp was about 2degC. The controller was set on 27 degC (women!) and the room was warm at about 25 degC (so the split was trying its heart out to satisfy them. The equipment distributor said that the warning lights indicated overcurrent and this could come about through maybe loose electrical connections, or maybe there was too much refrigerant gas in the system. The only other idea was maybe the high discharge pressures were stemming from the high desired temperature on the controller. I have an engineer calling in on Monday to check the terminals to make sure nothing is loose. He is certain that the fridge charge is correct, topping up only a small amount to cover the measured run, per specified rate/meter. That would just leave the high room temperature. Any other ideas of likely causes or things to check out?

momo
28-01-2007, 02:48 AM
Aaaah Midea - sounds like it's one of the dreaded low cost R407 heat pumps :eek: though I have not made acquaintance with it yet...
Yes, high room temp increases your "gas" line High pressure - less ref. condensing in the indoor unit... it can also push your amperage up - higher than for A/C: use a clamp meter and run the indoor fan at low/med/high allow a few minutes each time for stability of the system and compare.
Also check the outdoor fan: is it running all the time the compressor is running? (miss connected?)
Outdoor thermistor(s) used ? Ok ? connected (not replaced with a resistor?
Set at 27ºC - not unusual - because of low RH and perceived T. and also draughts and inadequate air distribution you get this or higher settings - check the room with a thermometer.

PS Was an adequate heat load calculation done
(insulation) ? You might find that a delta T of -25ºC
was not calculated adequate to the heat pumps
capacity - a delta T of 10ºC for cooling might have
been assumed and an A/C heat pump's efficiency goes
down when run near 0ºC.
Feedback on solution welcome:)

Andy
28-01-2007, 12:49 PM
Hi Makeit go right.
What about partially blocked indoor filters causing the head to climb.

Kind Regards Andy

Makeit go Right
28-01-2007, 03:06 PM
Thanks for your fast ideas. I will make sure the engineer includes these checks while there, tomorrow.

On the Room Unit, I was there on Friday and saw that there was some slight dirt on the filters but nothing that would obstruct the flow. I guess it all adds up together, and gets back to regular maintenance, which customer has declined so far (we will have more words on this after my engineer goes in there tomorrow/monday).

LRAC
28-01-2007, 05:46 PM
Hi Makeit go Right

If the initial checks are inconclusive i.e comp amperage, gas charge etc, try disconecting the indoor fan feed and running the out door unit, may help out on the diagnosis.

Regards
Lrac

Brian_UK
28-01-2007, 08:53 PM
Also, although the indoor unit filter may appear reasonably clear you also need to check the state of the indoor coil as well.

Makeit go Right
29-01-2007, 10:38 AM
Thanks for these further ideas. I will let you know if the engineer comes up with a result.

Brian_UK
29-01-2007, 08:31 PM
Thanks for these further ideas. I will let you know if the engineer comes up with a result.I suppose the other option of course is to get another engineer if all else fails :D

Makeit go Right
31-01-2007, 04:26 PM
That's right, of course, and I have a few more I can use. But he is quite good, so we will see how it goes.

Brian_UK
01-02-2007, 12:10 AM
Sorry MgR, brains going sideways tonight but my thoughts on your answer were....

Well if at first you don't succeed, sack one and try a fresh one....

Electrocoolman
05-02-2007, 01:07 AM
Come on Make It Go Right.....what was the outcome of the problem

Makeit go Right
05-02-2007, 10:21 AM
Hi, Electrocoolman.
I was not going to drop the string - it is just....well.....er...you know I said I was sending in an engineer that was "quite good," well, his van broke down on the way. It was towed off for 3 days of surgery, which messed up Plan-A.

I know the suspense is building up on this, but hold on for a few days more, eh? I will let you know then.

Makeit go Right
08-03-2007, 01:27 AM
I promised to get back to you and let you know what was the score. Well, it seems the engineer let too much (top-up) gas into the system when commissioning. Not a lot excess, so that all was well while on cooling. It showed up on the heating side with the high desired temperature, the rising pressure tripped the over-current protection.

Had the gas taken out and re-filled to correct quantity and there has been no problems since then (3wks ago).

{incidentally, the heat load calc - someone mentioned it a a possible area to check - that was okay. No worries there.}