HP cut out on roof top package air con!

[aquasanj]

Hi,

I have query about a roof top APAC reverse cycle air conditioner serving busy grocery shop. we have set it to run on heating as the shop gets too cold with the refrigerated display counters.

Temp set to 22 degrees, shop temp is close to 19 degrees. Ambient temp is 28-32 degrees weekly averages.

HP switch is factory set to cut out at 360 psi.

It trips out on high pressure now and again
Its a R22 unit and running pressures are within limit i.e 68 lp,240 hp PSI.

All filters are clean, indoor and outdoor fans are running and, running currents are within nameplate ratings.

Air flows are good with no restrictions in duct work.

The fresh air intake is fully closed via servo controlled dampers and the unit works on an economy cycle system whereby if outdoor temp exceeds 32 degrees, outside air dampers open and the compressor and out door fan go off and now the indoor fan recirculates the outside air.

I had feeling that during defrost (de-ice) cycle, the pressure might be rising above the 360 psi cut out which is factory set and tripping it. probably the de-ice control sensors or the de-ice time out circuit may need checking???

any advice on how i can test the de ice cycle, i thought of inserting the sensors in a frozen ice pack to emulate the cycle??

Of course it has to be monitored to confirm my doubt.

Any assistance will be highly appreciated guys.And a MERRY CHRISTMAS

cheers

[rude]

Hi,

I have query about a roof top APAC reverse cycle air conditioner serving busy grocery shop. we have set it to run on heating as the shop gets too cold with the refrigerated display counters.

Temp set to 22 degrees, shop temp is close to 19 degrees. Ambient temp is 28-32 degrees weekly averages.

HP switch is factory set to cut out at 360 psi.

It trips out on high pressure now and again
Its a R22 unit and running pressures are within limit i.e 68 lp,240 hp PSI.

All filters are clean, indoor and outdoor fans are running and, running currents are within nameplate ratings.

Air flows are good with no restrictions in duct work.

The fresh air intake is fully closed via servo controlled dampers and the unit works on an economy cycle system whereby if outdoor temp exceeds 32 degrees, outside air dampers open and the compressor and out door fan go off and now the indoor fan recirculates the outside air.

I had feeling that during defrost (de-ice) cycle, the pressure might be rising above the 360 psi cut out which is factory set and tripping it. probably the de-ice control sensors or the de-ice time out circuit may need checking???

any advice on how i can test the de ice cycle, i thought of inserting the sensors in a frozen ice pack to emulate the cycle??

Of course it has to be monitored to confirm my doubt.

Any assistance will be highly appreciated guys.And a MERRY CHRISTMAS

cheers

If your ambiant is 30degrees the unit shouldnt be icing up so i doubt defrost is the problem. Is the HP a manual reset or is it an auto one?

If its an auto* one and your pressures seem fine, i would change it. Ive had a few HP controls fail, just need to replace it and you should be right.


*By auto i mean its either welded in to the pipe work or schredder fitted and you cant adjust the setting.

[The Viking]

First of all,
It would be nice with more information, sub cooling/super heat/ delta Ts and so on.

But, you are in luck.
I think I know what's wrong here.
With ambients in the 30's my bet is that you are trying to run the unit well outside it's design envelope. Maybe it's even in the sun?
A baking hot evaporator will throw all the pressures sky high.

Not knowing anything about APAC but I bet they designed it for cooling with ambients of 5 to 35 *C and heating with ambients of -5 to 20 *C.


Just a guess of course... readings as per above would help pinning it down.

[aquasanj]

Thanks guys,

Dear Rude,

The HP switch is welded on to discharge line just before the RV.

Dear The Viking,

I will look up the operating and design conditions for this model and also revert with the other info you mentioned,

p.s the image on your web site is breath taking mate. good one.

cheers
Aquasanj

[acmechanic]

I think rude is on the money,

The auto HP's do fail from time to time. One way to test is to disconnect the fan and see what pressure the unit actually trips out on. You may fing the HP is tripping much earlier than the 360psi setting.

With the ecomony cycle, you could reduce the starting temp from 32 to 28 degrees to reduce the compressor run time?

[HVACRSA]

As far as I am aware APAC are designed in Australia so they should be able to handle a high ambient temp. I would also suggest checking the HP switch.

[eskimo2]

yeah it was not designed (and no standard system is) to operate on heating with 30 ambient....and i dont mean to offend here...but that should have been known by yourself and your supervisors etc etc etc

[nike123]

...................
I see now it is old post.

[kathysierra]

Hi,
The auto HP's do fail from time to time. One way to test is to disconnect the fan and see what pressure the unit actually trips out on.
Air conditioning maintenance and AC Repair should be done by professional service providers.

Hope it helps.

[jason09]

constant 32 degree air on evap coil any wonder pressures are high