Hitachi RAC-30CHA1 Reversing Valve Question

[dairytech]

Hi, I have a couple of questions to try to sort out a problem with a Hitachi RAS-30CHA1 / RAC-30CHA split system.

I'm no aircon serviceman, I fix printed circuit board's for a living ... so I dont know all the right terminology.

I got called in after 3 seperate companies had a look at the system and decided that it must be the pcb ... and all said "the pcb is no longer available ... buy a new aircon". :(

The symptons were that the machine would only blow hot air ... even when set to 16 degrees ... and all the techs said that the outdoor unit was ok, although one of them fitted a new reversing valve and coil.

After checking it all out and trying to understand how aircon systems work, I discoverd that the reversing coil could be operated by feeding it with 240 volts ... and then it would blow cold air.

For a while it looked like the board was at fault but eventually I tried the unit on heating long enough to find that it heated when set to cold ... and got cold when set to heating.

I then hoped it was a matter of reversing the 'reversing coil' connections (told you I dont know much about aircon systems) and discovered that made no difference.

So I assume that either the wrong type of reversing valve was fitted, or it was plumbed back to front.

My questions are ... can we simply invert the output from the pcb rather than have to pay someone (again) to come back in and change or replumb the valve. Seems like a much simpler (and cheaper) option.

Can a reversing valve be run backwards, long term ... assuming it has been plumbed back to front ?

Hope someone can help. Thanks.

[monkey spanners]

I think i'd fit a relay in the feed to the RV so it works correctly for the system.

I think the valves are available in normally heating and normally cooling varieties, so maybe the wrong type was supplied.

[stufus]

Check the inter connecting cables ,could be that the cooling and heating signals are crossed.A lot of the older systems used separate signal cables for heat/cool selection..
Cheers
Stu

[frank]

It's obviously been installed back to front.

The easiest fix is to fit a relay as Monkey Spanners suggests.

[dairytech]

Thanks for all the replies, you've put my mind at rest.

The interconnecting cables are only 4 wires (240V) .. Active and Neutral, and one each for the external fan and the reversing valve.

My first thoughts were to put a relay in the reversing valve line to 'invert' the drive as you are suggesting ... but then I found a spare drive channel in the IC that drives that line.

I fed the normal (low voltage signal) into the spare 'gate' which inverted the output before going off to the initial R/V relay.

Just had to cut the track, fit a couple of wires, plus an extra pullup resistor.

I really appreciate your help, as (not understanding how they operate) I was afraid leaving the wrong or backwards valve in could cause some harm to the works.

By the way, I was really surprised to find the actual circuit diagram in the service manual for this unit ... I'd probably still be scratching my head without it.

I have a couple sets of Daikin boards to fix too, but no such luck with circuits in their manual.

Thanks again for your help. :)

[stufus]

Glad you got it sorted.
Thanks for the update
Stu