Checking the Heat Pump

[Petertaylor]

Our York system works fine—heat pump in summer and LP gas in winter. Knowing that auto AC systems can get low on refrigerant, I wondered if that happens on household systems. I called the installer who put it in 10 years ago and asked him to check it out.  I expected him to hook up some gauges and read hi/Lo pressures. 

He said we don’t do it that way anymore. He went to the furnace in basement. With the system calling for COOL, he measured the air temp on both sides. “Twenty degree difference, that’s as good as it gets. Your system is fine.” 

I only post this because I found it interesting to see how he confirmed it is okay.

[blackhat]

Would you walk into your doctor’s office and ask him to slice your belly open and have a look at your appendix because you’re not sure if it’s ok?

Yeah ok, that sounds extreme but it is analogous. If you thought you had a tire with low pressure, would you check the pressure or dismount the tire and check it for leaks?  Start simple, if there is no evidence of a problem and performance is what it should be, why go further?  

There’s actually 2 schools of thought within the trade. Old school was throw a set of gauges on and work from that. The problem with that approach is that every time you put gauges on, a few ounces of the system charge end up leaving with the gauges. Do that a few times and the system is short a half pound and now it is not working efficiently. The refrigerant system is meant to be sealed and gauges are intrusive. My gauge manifold is a critical tool in my arsenal but it isn’t a magic decoder ring and often isn’t necessary. As a 40 year veteran in the trade, I am actually encouraged to hear of a tech using system performance instead of a crutch, particularly if there are no symptoms of problems.

[Snipe Hunter]

Our York system works fine—heat pump in summer and LP gas in winter. Knowing that auto AC systems can get low on refrigerant, I wondered if that happens on household systems. I called the installer who put it in 10 years ago and asked him to check it out.  I expected him to hook up some gauges and read hi/Lo pressures. 

He said we don’t do it that way anymore. He went to the furnace in basement. With the system calling for COOL, he measured the air temp on both sides. “Twenty degree difference, that’s as good as it gets. Your system is fine.” 

I only post this because I found it interesting to see how he confirmed it is okay.

When I inspect houses, I do the same thing. I check the delta between the supply and the return. 20ish degree delta, it's working. 90% of the time I call out the disintegrated insulation on the suction line and dirty condenser coils... and more mold in the evaporator cabinet and coil than one might expect. If it's not cooling right, I don't pretend to know why. It's busted.

[MstrCarpenter]

Would you walk into your doctor’s office and ask him to slice your belly open and have a look at your appendix because you’re not sure if it’s ok?

Yeah ok, that sounds extreme but it is analogous. If you thought you had a tire with low pressure, would you check the pressure or dismount the tire and check it for leaks?  Start simple, if there is no evidence of a problem and performance is what it should be, why go further?  

There’s actually 2 schools of thought within the trade. Old school was throw a set of gauges on and work from that. The problem with that approach is that every time you put gauges on, a few ounces of the system charge end up leaving with the gauges. Do that a few times and the system is short a half pound and now it is not working efficiently. The refrigerant system is meant to be sealed and gauges are intrusive. My gauge manifold is a critical tool in my arsenal but it isn’t a magic decoder ring and often isn’t necessary. As a 40 year veteran in the trade, I am actually encouraged to hear of a tech using system performance instead of a crutch, particularly if there are no symptoms of problems.

Hey Blackhat,
is there a scenario when you would check/verify performance by temperatures of the high and low lines at the compressor? How about current draw? I (now, thank-you) know delta T is a pretty good indication of system performance, but we're also interested in efficiency too, right?

Last week I was asked to fix a Mitsubishi mini-split that I installed three years ago. On the ride over I'm contemplating what I can actually troubleshoot because these units are getting more and more complex and I don't work on them often enough to keep up. I mean it's getting to the point that the only way to ensure you have the right charge is to evacuate the system and weigh in the specified amount. But this one was easy. I didn't even want to learn how to use the remote, so I asked the customer to turn it on high. Ten seconds later I handed her the filter and told her to wash it in the shower while I poured a cup of coffee. Took two sips, reinstalled it, and said; "Thanks for the coffee. It's fixed."

[Roly]

Hey Blackhat,
is there a scenario when you would check/verify performance by temperatures of the high and low lines at the compressor? How about current draw? I (now, thank-you) know delta T is a pretty good indication of system performance, but we're also interested in efficiency too, right?

Last week I was asked to fix a Mitsubishi mini-split that I installed three years ago. On the ride over I'm contemplating what I can actually troubleshoot because these units are getting more and more complex and I don't work on them often enough to keep up. I mean it's getting to the point that the only way to ensure you have the right charge is to evacuate the system and weigh in the specified amount. But this one was easy. I didn't even want to learn how to use the remote, so I asked the customer to turn it on high. Ten seconds later I handed her the filter and told her to wash it in the shower while I poured a cup of coffee. Took two sips, reinstalled it, and said; "Thanks for the coffee. It's fixed."

"Hey Blackhat,
is there a scenario when you would check/verify performance by temperatures of the high and low lines at the compressor?  "  
 I was wondering that also, but you would need ambient temps included in the formula.    I ran some test line temperatures but at the inlet and outlet of the inside coil.  Roly 

[blackhat]

Line temperatures can be used as part of a diagnostic test and during initial set up. It’s a part of setting or determining system superheat or sub cooling but only a part of those tests. 

Amp draw is useful for diagnosing individual motors or heaters within a system but there are 3 motors. 

Inverter based mini splits can be a challenge. The three motors are all running at a system selected speed based on control inputs and conditions. You would need a massive chart of data points and then try to intersect at least 3 curves to determine performance. 

If a system has been properly set up at install, and there are no observed issues, the delta T is a solid indication of performance. Efficiency is tied to that fairly tightly.

[MstrCarpenter]

Line temperatures can be used as part of a diagnostic test and during initial set up. It’s a part of setting or determining system superheat or sub cooling but only a part of those tests. 

Amp draw is useful for diagnosing individual motors or heaters within a system but there are 3 motors. 

Inverter based mini splits can be a challenge. The three motors are all running at a system selected speed based on control inputs and conditions. You would need a massive chart of data points and then try to intersect at least 3 curves to determine performance. 

If a system has been properly set up at install, and there are no observed issues, the delta T is a solid indication of performance. Efficiency is tied to that fairly tightly.

This is what I was referring to. When they move heat, but not enough, is when I ask myself; "O.K. where do I start?"

So line temp.s aren't really useful because the system may already be self-compensating for low refrigerant or clogged filters? This was a lot easier in the 1980's. Of course that was before internet so I had to go to the Library or find an older technician who had enough job security to not feel threatened by sharing his knowledge. A few months of classes and a certificate alone don't too far.