Heat pump running in a vacuum

[kchest4063]

Another technician at our company installed a new compressor in a Lennox Heat Pump the other day, wired it up, weighed in the charge and was testing the unit. He said it ran OK for a short time, then the low side pressure started dropping until it went into a vacuum. He said the high side pressure stayed around 110 psi or so while he had it on.

As it turns out, I'm supposed to go out there in the morning to figure out what went wrong.

Any ideas?

[rbiebr]

Sounds like possible TXV problem

[dandyme]

if that's all the info you were given, just start from scratch. make sure what is operating is operating correctly.

then start determining what isn't doing what it's supposed to be doing.

there's a good indicator of what took out the compressor

is there a specific reason the tech didn't/couldn't determine what the problem is

[martyinlincoln]

Plugged up drier or crap in the txv would be my guess.

[kchest4063]

Thanks for the quick replies. The tech that went out is pretty new, it was late in the afternoon Saturday and I think he just gave up.

As I understand it, the old compressor was shorted to ground, and I'm pretty sure he didn't check the TXV before or after the compressor install.

[BaldLoonie]

Other than looking for a broken capillary or equalizer tube, you can't tell a bad TXV without a working compressor! Likely it was what took out the first one.

[garyed]

It sounds like a total restriction probably at the metering device but there could also be a serious leak where the gas is escaping almost as fast as it went in. Of course if its a leak that bad there will probably be no gas in the system when you get there.
This brings up an interesting point.
How do you tell the difference between low refrigerant & restriction.
Normally with a restriction your subcooling will be high but if the restriction is bad enough it may not be, plus you don't want to bypass an LP switch & run the system in a vacuum too long to measure your liquid line temp. The easiest way I know is to weigh in a couple lbs. of gas & see what happens. With the cost of R22 that's not the greatest way any more so I'd like to hear what others do in the same situation. How can you be sure you have a restriction before opening up the system?
High SC & high SH is one way but is there another?