Extrenal e.q Valve on static comp

[minusdegrees]

I came across a W/I freezer (r409) that I diagnosed as having a bad comp. I replaced compressor... recharged unit to ...Was getting high suc. pressure and low head pressure.....This unit was on a high roof .... I went down stairs to check the evap ... fans not running ......had to by-pass defrost termination switch to get fans to come up ... need to replace that component too..suc pressure dropped slightly ...ok ... here's my question.... I front seated the external e.q valve as..... i did the suc pressure dropped ... 10 to 12 psi where I needed it .... but box temp was still 35 + degrees... and not dropping ... How do I charge a system w/ an external e.q valve......

[R12rules]

Welcome to the forum.

409 is a blend. It is a drop in for R12 medium temp applications only.

It has no value in a low temp setting. Perhaps you meant 408? That is the drop in for R502.


You said you replaced the compressor. ok.

You said you were starting up the system and theunit cooler fans, evaporator fans, they didnt come on until after you jumped out the fan delay switch.

Those fan switches dont usually close until the temp on the side of the evaporator coil is fifteen degrees above zero.
Soooooooo .... I figure your cooling capacity wasnt coming down low enough to bring on the fan switch.

You said you droped the suction pressure down to 10 or 12 PSIG. Which is where you said you needed it to be running at.
Well, that would be a low back pressure if the system was a medium temp R409 system, and not a low temp system.
Please define this "external e.q valve".


Somethig just isnt right here.

It appears you have the wrong freon for the application.


Need more info.

[icemeister]

The next time you run into an old R12 LT system with a bad compressor, just replace the whole condensing unit and the TXV to R404A and be done with it.

On this job however, I agree with R12 that R409A isn't the best for a LT R12 replacement. Use MP66 (R401B).....it's a lot better for freezers.

When you said you "front-seated" the externally equalized valve to bring the suction pressure to 10-12#, do you mean to say you crank the TXV adjusting stem all the way in? If so, that's not the right thing to do with any TXV......they're not pressure regulators. A TXV is essentially a superheat regulator.

As far as the rest of your problem goes, it's best for us out here in Cyberland not to start guessing as to what you've got to deal with. Provide ID for the compressor, evap and TXV, operating pressures, superheats, etc and we can talk. Does this sytem have a CPR valve or MOP power element on the TXV?

BTW, this thread should have been posted in the Refrigeration & Icemaking section to get a lot more responses.

[Edited by icemeister on 07-23-2004 at 07:29 PM]

[minusdegrees]

Thanks for all the advice it is a great help ....

Further description of unit ...and situation...

My definition of this eq.... valve....External eq.... it was located on th suction line aprox 18" from the comp.../ condensing unit on the roof... or is it called a CPR valve?
Yes I aggree with 409... not being appropriate for low temp stuff... this was not a very old cond unit either... and the sticker on cond. said 409 .....So ... Thats what I went with ... in future I will follow the advice of using 408.... or mp66......as for TXV (I did no adjusments to it down stairs ....waiting for unit to drop temp before making any TXV adjustments) just the one on the roof....I suppose I'll need to start over w/ different refrigerant.....I'll let you know

[R12rules]

You just might wanna re-adjust that CPR valve back to it's original setting.

You dont want to running the system with it cranked down like that.

MP-66 sounds like a greeeeaaaaaat idea!!!