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paul441
15-09-2010, 08:34 PM
Hi
I am new to the fridge game and will be working on dryers, can you tell me how i understand what the pressures should be when i stick my gauges on suction and discharge ports. ie if i know theres enough gas in system.
cheers.:confused:

glenn1340
15-09-2010, 09:01 PM
Hi Paul,
Do you mean compressed air dryers? It all depends on what gas is in the system, most of the smaller ones are 134a and the larger 407c, and if it`s a thermal mass dryer. I`ll try to post the relevant pressures/temps tomorrow after I`ve checked my tech books as I don`t want to give incorrect ones off the top of my head.

paul441
15-09-2010, 09:26 PM
Hi Glen
yes it is compressed air dryers mainly 134a 407c and 404, thanks for your time and help.
cheers

glenn1340
16-09-2010, 07:06 PM
Hi Paul,
Here are the pressures I`d expect to see on typical `fridge dryers:
R134a low side approx 2.2 to 2.5 bar this would give a dew point of 2c to 6c and the high side around 10 to 12 bar, this being controlled by the fan pressure switch if the dryer has one. Otherwise it will be a constant run fan and the hight side will vary due to ambient conditions. These are usually the vary small dryers to suit 10kw compressors and below.

R407c:
Low side 3.8 to 4.6 bar to give the same dew point and 15 to 18 bar, once again controlled by the fan pressure switch.

On a thermal mass system the low side can easily run at 1.5 bar on 134a and 2 bar on r407c or thereabouts, as the refrigerant is cooling a "storage" block that in turn cools the air. Therefore a lower refrigerant temperature will result in the storage mass cooling quicker and in turn cooling the compressed air. The dew point is controlled by a temperature probe inserted in the storage mass. When the dew point reaches it minimum setting the compressor cuts out saving energy untill the temp of the mass rises to its max setting and brings in the compressor again. By the way on most thermal mass dryers there`s a start delay of around two minutes to allow the pressures to equalise after stopping. If you`re unaware of this it can result in thinking there`s a fault (er....I know, I`ve been there...duuuuh)
All the above can vary due to dryer make
On constant non thermal mass dryers the low side is controlled by the capillary tube and more often than not (on larger dryers) a hot gas valve that responds quickly to varying compressed air temperatures so preventing the condensate from freezing and blocking the dryer. This, in fact is an indication that the dryer my be low on refrigerant. When the dryer is switched off the ice will melt and the air will flow again untill the cycle is repeated and freezing re-occurrs. Other signs of low refrigerant are cool discharge pipe from the compressor, the high side pressure failing to rise significantly, high super heat and or low superheat; and the most obvious, signs of oil residue on joints etc.
I hope this helps.

Regards,
Glenn

paul441
16-09-2010, 08:20 PM
Hi glen
Thats very helpful info,thanks for your help. I have a dryer problem at moment that im looking at saturday when i last went to it ,but didnt have enough time, it was showing dp of 28 comp was very hot not sure if fan was coming in but when put gauge on lowside needle on gauge shot right round,only lowside port on it,also had switcth not sure if it was hp or fan .any help on that cheers mate

glenn1340
16-09-2010, 09:44 PM
Hi glen
Thats very helpful info,thanks for your help. I have a dryer problem at moment that im looking at saturday when i last went to it ,but didnt have enough time, it was showing dp of 28 comp was very hot not sure if fan was coming in but when put gauge on lowside needle on gauge shot right round,only lowside port on it,also had switcth not sure if it was hp or fan .any help on that cheers mate

Hi Paul,
With a high dew point and the low side pressure very high and compressor very hot, first thing I`d check is the fan operation. Turn the power off and see if the fan spins ok, I`ve lost count of the times a similar faults been caused by a siezed fan especially those low wattage alloy ones.
You say you`re not sure if the switch is a fan or HP. Normally a HP switch on a dryer has a manual reset unless it`s a more complex control system with trip relays etc. Try linking the switch out to see if the fan comes in, if it does and the low side drops with a fall in the dew point that could be the problem.
I`ll never understand why schreader valves aren`t fitted to the high side on all equipment as the price is minimal and they make diagnosing faults so much easier.

What make and model is it by the way.

p_p
17-09-2010, 09:04 AM
Hi Paul

I have been working on dryers all my life and all manufacturers kit yourself up with a good set of guages and a comparator. An essential piece of kit when setting up a drier.
After a while the operating pressures of the differant refrigerants will become second nature.
Are you working for a contractor or manufacturer.
Dryers can be a bit daunting when first starting out but once familiar with how they work they are actually very very simple in there operation.
Any probs please post we are all here to help.

Good luck

PP

paul441
17-09-2010, 05:53 PM
Hi glenn
Thanks for your help,its a integeral in an atlas copco air compressor , GA11 small one , dryer only takes about 0.70kg. thanks again for your help

paul441
17-09-2010, 05:57 PM
HI pp
I am employed by a company and they mainly deal with atlas copco dryers integeral or free standing.thanks for your help, cheers

paul

coolhibby1875
17-09-2010, 07:02 PM
Hi glen
Thats very helpful info,thanks for your help. I have a dryer problem at moment that im looking at saturday when i last went to it ,but didnt have enough time, it was showing dp of 28 comp was very hot not sure if fan was coming in but when put gauge on lowside needle on gauge shot right round,only lowside port on it,also had switcth not sure if it was hp or fan .any help on that cheers mate

if the compressor was running and your manifold shot right round, i would guess the compressor is shot, passing between valves

monkey spanners
17-09-2010, 09:34 PM
If the evaporator leaked on one of these, would it fill the fridge system up with air?

Just wondering about the suction gauge shooting right round.

glenn1340
17-09-2010, 11:31 PM
If the evaporator leaked on one of these, would it fill the fridge system up with air?

Just wondering about the suction gauge shooting right round.

Good question that. I have come across it before but very rarely. If it has leaked the dryer`s a scrapper for sure as evaporators are rarely economical to replace.

the chiller
22-11-2010, 04:58 PM
comp sounds shot am afraid mate