Heat pump testing in summer

Bob Spermo · 07-28-2009, 06:58 AM

Is it wise to check a heat pump in the normal heat position when the temperature is over 90 degrees? I have had HVAC technicians tell me it is a bad idea to check them in the heat postion when it is over 70 degrees.

Similar Threads:

**Scott Patterson** · 07-28-2009, 08:20 AM

In the summer I just check the cooling mode and then the supplemental heat. If it is cooling in the cool mode it should heat in the heat mode. After all a heat pump is basically an A/C with a reversing valve.

**Jerry Peck** · 07-28-2009, 09:34 AM

Originally Posted by Scott Patterson

In the summer I just check the cooling mode and then the supplemental heat. If it is cooling in the cool mode it should heat in the heat mode. After all a heat pump is basically an A/C with a reversing valve.

It will only heat if the reversing valve works.

I would test the a/c system first (it is on anyway) then when through with the a/c system, switch it off, switch to heat, and make sure heat comes out. If heat comes out, the reversing valve is working and there is no need to run it to see how well it runs as you already checked that under a/c operation.

Then switch to off, then switch to cool ... it is not nice to leave it on heat and forget about it.

**Scott Patterson** · 07-28-2009, 10:42 AM

Originally Posted by Jerry Peck

It will only heat if the reversing valve works.

I would test the a/c system first (it is on anyway) then when through with the a/c system, switch it off, switch to heat, and make sure heat comes out. If heat comes out, the reversing valve is working and there is no need to run it to see how well it runs as you already checked that under a/c operation.

Then switch to off, then switch to cool ... it is not nice to leave it on heat and forget about it.

That is true, but every single HP manufacturer that I have seen their guidelines recommend not operating in the heat mode when it is warm outside. Now if it has a Scroll compressor I don't think that they can be damaged like a conventional piston compressor.

**Jim Luttrall** · 07-28-2009, 11:00 AM

I too, test the heat just to see if it switches and begins heating then switch to the emergency setting to test the supplemental heat.
Beware though, damage can result from operating in the heating mode too long. The suction temperature and pressure are too high and will create a high amp draw on the compressor as well as over heating of the compressor. I rarely leave the compressor on for more than a minute or two during warm season testing.

**Jerry Peck** · 07-28-2009, 11:05 AM

Originally Posted by Jim Luttrall

I too, test the heat just to see if it switches and begins heating then switch to the emergency setting to test the supplemental heat.
Beware though, damage can result from operating in the heating mode too long.

Yes, not too long, but it does not take long to make sure it heats and the reversing valve works.

I don't recall how long I let them run, maybe a couple of minutes or so, never had one fail and never had a problem, just knew that I should not let it run "too long" on heat during the summer.

**Vern Heiler** · 07-28-2009, 12:04 PM

Running a heat-pump in heating mode in the summer is no different than cooling a very hot house. A scroll compressor can take a little slugging or liquid without damage but during heavy load slugging is not an issue. The liquid line will not get hotter than the ambient condition of the outdoor coil (air temp and radiant heat from sun) so the vapor will not be HOT on the compressor, but not as cool as from a cooled condition house.

Some of the logic in requiring voltage to switch the valve into cooling mode is people can go without cooling but don't do well without heat.

**Jerry Peck** · 07-28-2009, 12:15 PM

Originally Posted by Vern Heiler

Some of the logic in requiring voltage to switch the valve into cooling mode is people can go without cooling but don't do well without heat.

Also, the code *requires* the ability to *heat* a house, it does not require the ability to *cool* a house.

Lack of heating is a code defect as well as a functional defect, whereas lack of cooling is only a functional defect.

**Matthew Barnicle** · 07-28-2009, 12:43 PM

I test the heat also...just long enough to make sure the reversing valve worked. I also wait at least 10-15 minutes with the cool/heat/off setting to "off" before switching over. During the 10-15 minutes between cool and heat, I am running the fan in the "on" position in order to get the coils up to at least room temperature. I worry about rapid expansion and contraction of the coils from cold to hot more than I worry about anything else. I don't recall ever finding a reversing valve that didn't work. Has anyone? If it is extrordinarily rare, I suppose it is not worth the risk to test it.

**Vern Heiler** · 07-28-2009, 01:12 PM

Originally Posted by Matthew Barnicle

I test the heat also...just long enough to make sure the reversing valve worked. I also wait at least 10-15 minutes with the cool/heat/off setting to "off" before switching over. During the 10-15 minutes between cool and heat, I am running the fan in the "on" position in order to get the coils up to at least room temperature. I worry about rapid expansion and contraction of the coils from cold to hot more than I worry about anything else. I don't recall ever finding a reversing valve that didn't work. Has anyone? If it is extrordinarily rare, I suppose it is not worth the risk to test it.

The coils are shocked everytime there is a defrost cycle in the winter, no problem then, so why would there be a problem with going straight to heating in the summer?

Typicaly what fails is the thermostat or wiring. Transfer valves do fail but it is rare.