Hot Day/ High Head Pressure

[Evapman7]

I have been working in the trade for nearly a year now and have a question on something which puzzles me. So any help would be grateful.

Why is it that in the Uk when we have a nice hot summers day there seems to be a lot problems with units tripping out on high head pressure. I know not every unit does this but no matter which make or model when are temperature picks up we seem to have problems. But say we compare these units to models anywhere abroad i.e Spain,Greece,Turkey. Why do they not suffer the same problems because surely there ambient temperature is always a lot higher than the Uk.

[chemi-cool]

Because in the UK, you use too small condensers instead of using bigger ones with more fans.
Thats why!

And every year we get the same posts about the "hot British summer"

Do me a favor, we deal with 45°C all summer without problems.

[Evapman7]

Granted you many have a couple of degrees more on us in the summer :P But surely we cant just go changing the size or a condenser.This will only cause problems else where. Or if we increase the size of the whole system then surely we will have problems with the unit being "oversized" for the room?

[nike123]

Granted you many have a couple of degrees more on us in the summer :P But surely we cant just go changing the size or a condenser.This will only cause problems else where. Or if we increase the size of the whole system then surely we will have problems with the unit being "oversized" for the room?

Are you talking about split-system air conditioners?
What brand you dealing with?

[Evapman7]

Most of the time split systems yes. No brand in particular any of the following really mitsubishi, Fujitsu, Daikin.Say a 7kw wall mount in a office area (uk). Surely we could not have the same 7kw unit in Spain.

[nike123]

Most of the time split systems yes. No brand in particular any of the following really mitsubishi, Fujitsu, Daikin.Say a 7kw wall mount in a office area (uk). Surely we could not have the same 7kw unit in Spain.

Mitsubishi, Fujitsu, Daikin should handle easy your ambient temperatures. I, here, newer have problems with them and our temperatures are sometimes 42°C.
How about correct placing outdoor unit with enough clearances and without obstacles. Also do you have lot of debris in the air and dirty condensers. Their fins are pretty dense, and if air is full of dust it becomes easily clogged.
Clean them often.

[airefresco]

I know what he´s trying to say. When I worked in England, as soon as summer came along the phone never stopped ringing, and a lot of time it was units tripped on H.P. Here in the Canaries, where it´s above 20ºC all year round, I very rarely find a unit tripped on H.P. Even in summer when it reaches 40ºc +.

My theory is that in the UK the unit´s only really have to work hard on those really warm days, and there´s not that many of them. So when the temperature goes up, all the units that were ready to break, all do at the same time. Here and in other warm countries, the units have to work hard all year round, so as soon as problem develops, the fault is shown immediately.

I think there are possibly different models also for warmer climates. The Daikin UK catalogue and Daikin Spain catalogue have/had different ratings for the same units. And our units come from the Japan factory not the Belgium one.

[Brian_UK]

I think the important thing has already been said by Nike..

Make sure that the condenser coils are clean.

[Thermatech]

Most Japanese split systems sold in the UK are rated up to 45 deg C ambient.

So if a unit trips on HP at less than 30 degC ambient then there is a problem which should be identifiable.

Its the service engineers job to locate & resolve that problem.

BTW is this a problem with all refrigerant types or only one refrigerant?
Do the units run flat out cooling & do not stop because they never get to set point ( undersized ) or do they constantly stop start because they do reach set point ( oversized ) ??

[philfridge]

Its down to lack of good maintenance ie cleaning condensers setting hp controls correctly etc which is not being done. Then when it warms up the units are not ready for the heatwave

[Argus]

Granted you many have a couple of degrees more on us in the summer :P But surely we cant just go changing the size or a condenser.This will only cause problems else where. Or if we increase the size of the whole system then surely we will have problems with the unit being "oversized" for the room?

Consider that most of the split systems on sale in the UK are designed and made for semi-topical climates, where 30 – 40 degrees is the norm.

Then they are installed in a UK city, usually in the winter months and expected to cool in ambient as low as 10 degrees sometimes peaking at 35.

In my experience, most split AC units are charged at site in the cooling mode on relatively cool days and are invariably overcharged as a result.
This has the effect of stacking the ‘spare’ refrigerant in the outdoor coil, and giving a partial solution to over-condensing in the winter – remember, these things will probably be still cooling over-heated offices in the winter months. (sounds stupid, but that’s what happens).

Switch the scenario to the summer when the temperature may creep up to 35. Moderate by the standards of some countries, but an overcharged and partially full condenser will contribute to the symptoms you’ve described.

Add to that, dirty coils, poor outdoor unit siting that re-circulates condenser air…… etc.





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[GXMPLX]

When noise and tight space to install are the primary concearns, warm air recirculation becomes a big issue. You can get by in normal weather but it might get you in a hot summer. Place a thermometer in the AIR INTAKE of the condenser try to insulate it from sources of thermal radiation. If from system start this temperature never stops rising until you get a trip, you're having warm air recirculation. The prase "warm air rises" is only valid if you have no external pressure differences like a sucking fan creates.

[US Iceman]

As Argus alluded to, the units are designed for a certain operating range. If those units are placed into operation in a location, where external factors can affect the performance of the unit the system will simply not perform adequately.

In other words, the unit performance is being affected or controlled by some factor that it simply was not designed for.

It does not make the unit bad, it means the installing person (or sales person) did not fully consider the ramifications of these factors. Most likely because they did not know, did not understand, or were afraid the cost would increase if they did the job properly.

[Sridhar1312]

Normally any location before summer all the settings like High Pressure need to be checked and set for summer conditions. If the above is not done it will trip.