Walk-in freezer high head pressure

[zuke19]

I have a r-404 unit remote, condensing unit on roof running at 350 on high side with about 134 sat temperature and on the low I have 4 deg sat temperature
with the flip cover off and the outside roof temp near 100 deg, box is at 20 deg. I blew out all the dirt out of the condenser, and there was plenty, the high side does not sit still, it will fluctuate from 330-390, kicks off at 400, when it starts up, the high side immediately goes up for 5-10 seconds and nearly pops at 400 before coming down
when I put the top down, the head pressure raises to 400 and kicks off, and has been cycling on that, thought possibly overcharged so I let some gas out till few bubbles in glass, now I am thinking moisture or noncondensables in system but my suction seems normal. I left cover part way off to keep pressure from rising, air only blows out back of cover and fan seems to want to push it out sideways so the air stays in the condensing unit longer, has been like this for several years though, anybody got anything.

[VTP99]

Your going to have to clean that coil better then blowing it out. Get some Nubrite coil cleaner and a pressure washer to clean it good. Also is the fan on a cycling switch ?

[Wheelbaron]

First cool the CU down once with water, then try pumping down the compressor. Could be a bad discharge valve. If that is not it, it could be an uneven mix of 404, or non condensables. Recover and charge with fresh juice.

[zuke19]

First cool the CU down once with water, then try pumping down the compressor. Could be a bad discharge valve. If that is not it, it could be an uneven mix of 404, or non condensables. Recover and charge with fresh juice.

freezer now down to 8 deg with cover the way it is, and it is raining here though, if I had a bad discharge valve, wouldn't I have higher suction pressure, and the pressure wouldn't drop on suction right because it does drop

[zuke19]

Your going to have to clean that coil better then blowing it out. Get some Nubrite coil cleaner and a pressure washer to clean it good. Also is the fan on a cycling switch ?

no unit has head master, no cycling switch I believe but would have to recheck that, headmaster seems to work fine, checked line going into control and it was not hot so condenser should be in play

[kklobas]

you have a few choices for very high head pressure- overcharge, air in system,dirty coil, lack of airflow.

i would wiegh out charge, and pull a good vaccuum, then recharge to correct level. Also wash the coil very well, and use a good coil cleaner. If fan is running correctly, and you do those two things, you have pretty well addressed all common causes

[2sac]

Your going to have to clean that coil better then blowing it out. Get some Nubrite coil cleaner and a pressure washer to clean it good.

Start here. If you have to, pull the fan and blow it out again from the inside, then wash I have also pulled the louvers off the covers and replaced with chicken wire to make sure ALL the air is being discharged from the unit. Once this is in order, you can then make the proper diagnosis if needed.

[jackintheboxtec]

Sounds to me like you need to clean that condenser real good before you do anything else!

[pr0dukt]

This is an odd one but my head keeps circling back to non condensables as well. Like you're periodically freezing up the valve orfice or drier, enough to kick that head pressure way up. But you would see some fluctuation in suction pressure too, unless lineset is obscenely long. And even then. It's not your discharge valve if you can pump it down with no issues.

Sight glass telling you anything moisture wise? And if you pump it down at the receiver and not the solenoid, can the receiver hold everything without tripping high head? And what's you're txv and distributor doing? Frosting at all? Drier colder on one side during a cycle? Compressor smoking hot or still touchable without getting 3rd degree burns? No EPR or CPR on the suction line right? (Would be a detail I'd hope you'd include =p) and what type of compressor? Recip?


Edit# some how overlooked the post you mentioned it has a head master. <_< take an actual temp reading across those lines from inlet of HM to inlet of receiver. Be SURE that is not dumping hot gas into the receiver. Some times its not obvious by quick touch of each line. And if it going into condenser. Braze a saddle right after condenser coil, Ignore receiver service valve, and take a sub cooling measurement. Should tell you how well your condenser is dispelling heat or if you're overcharged. Assuming the headmaster is even working correctly. You have to be held up somewhere if your charge is good. Condensers get plugged from time to time as well. If you clip the headmaster and watch your head sky rocket into oblivion, then your coil is garbage.

[2sac]

The HPS is also set a little low @400psi

[ga-hvac-tech]

Clean first...
Airflow second...
Then troubleshoot.

Problem is... if the first two are not right... fixing the third or fourth or fifth (etc) will not fix the unit...

[pr0dukt]

And yes all my previous ramble is under the assumption the coil is ACTUALLY well cleaned and you have straight air flow through. Which I'd hope is the case. ::face palm::

[Wheelbaron]

Check your amp draw, a bad discharge valve will still show good suction pressures, but the comp will over heat, and the head press will be high and amp draw will be high. And there will be an over all loss of capacity.

[frank slusher]

Go with the dumb s#$$@ first, turn off the power drag a hose to the unit and wash the crud out of the coil. I was talking a tech through a the same problem not long ago. He removed the charge, recharged with new 404a, adjusted the txv to who knows where, talked to tech support and they instructed him to replace the head master and txv. Box was at 10 when he started customer wanted -10, 10 hours later box was at 40. He hasn't done much refrigeration and we were really busy, had I known he was close by would stopped over to check on him. Coil looked clean on outside, but fan blades were filthy. Another company had just finished cleaning the coils on the entire strip. You couldn't see any light through the coil and when he sprayed it with nubrite the dirt started rolling out of it. We topped off the charge and it was fine. When you ask for help, the person on the other end assumes that you have exhausted the simple things first.

[lytning]

Would a simple thing include checking the dryer? Has any one changed the fan blade? Is the suction line sized right?

[aprophet]

Would a simple thing include checking the dryer? Has any one changed the fan blade? Is the suction line sized right?

Lota techs don't think to see if the fan blade is turning in the right direction little thinghs missed wind up being your headache

[SandShark]

I left cover part way off to keep pressure from rising, air only blows out back of cover and fan seems to want to push it out sideways so the air stays in the condensing unit longer, has been like this for several years though, anybody got anything.

I'm a little confused by this statement. Is air being pulled through the condenser coil and blown through and across the compressor or the other way around?

[VTP99]

I'm a little confused by his statement. Is air being pulled through the condenser coil and blown through and across the compressor or the other way around?

I am visualizing a cover for a outdoor unit,solid sides and open at the front and back.
OP says " air only blows out back" so all that sounds right. Now the part I don't understand is "fan seems to want to push it out sideways" is there no shroud ?

[2sac]

"fan seems to want to push it out sideways"

I missed that the first time. When you have a plugged condenser coil on an A/C unit, when you run your hand over the fan discharge, which way does it push the air? Up? or out the sides.....

[pr0dukt]

Out the sides around the parameter of the blade. If its clean you will feel it blow straight through the coil and straight onto the compressor. Assuming its directing behind where the fan motor is mounted like on most walkin condensing units.


If air is blowing out the sides of the fan blade. Coil is clogged.

Had one yesterday at a bakery full of flower and other powders. Literally baked a cake inside the coil 0. No air flow through and burnt up the compressor. Good times.