Suction/Discharge pressures equal

[MTC(SS)]

I have been stumped on this problem for a few weeks now.  I completed an HVAC course last year, but mainly for my own benefit on my rentals, so I don't get a ton of experience. 

 

  The tenant has complained about low heat from the heat pump.  The system is about 10 years old R22. I'm not real familiar with determining subcooling/superheat during the winter with the low ambient temperatures.  However, I thought I would get the measurement anyway.  When I attempted to determine them, I put my gauges on the system, and both sides were equal (yes, my manifold valves were shut).  I switched heating to cooling and the pressure rose, but was still equal between the sides.  I didn't even bother to determine the SC/SH. 

 

  The suction and discharge lines were significantly different temperatures, and when placed in heat mode, the normal suction line (larger tube) was indeed hot and heat was being put into the home. 

 

  I've read some posts from previous years that members have commented on and several mention the reversing valve.  This may be a factor.  I am in N. Florida so lately, some days we may still place the system in cooling mode.  It seems to cool well in cool mode.  My thought is that it would be a failed metering device or compressor, since these are the  components that separate the pressures. 

 

  I have not checked the compressor draw and know I need to, but the equal pressures with temperature differential on the suction and discharge through me for a loop. 

 

I'm not thrilled about it, but at this point I think I need to recover the refrigerant, replacing the filter/dryer of course, and the metering device.  I think that if it were the compressor there would be no temperature difference.. 

 

Any help... Thoughts... ideas... would be appreciated.

 

Thanks.

 

[BryanS]

I haven't really messed with gauges on a heat pump during heat mode, but I think you are supposed to have your low side gauge on the true suction port and not the actual suction line port. It should be behind one of the panels or near the other ports. It's different depending on the brand. The true suction port is always low side no matter what mode, so I was told to always hook up there when getting my pressure readings. Remember a heat pump reverses direction in heat mode. If I'm correct and you check from the suction line port and liquid port, then you will get the same pressure. It's like checking from the discharge port of the compressor to right before the evaporator. The pressure would be identical. Your inside coil is now the condenser so the refrigerant pumps from the compressor, through the 3 way valve, through the suction line (high pressure vapor/liquid), through the indoor coil(condenser), through the liquid line, into the metering device, and then the outdoor coil(evaporator) on it's way to the compressor. The way it seems to me it passes as a high pressure through both service ports, so you will get identical pressures. Hook up to the true suction port for the low side this time and see what you got. If I'm wrong, so be it. Most of my hvac experience is on my own, but I have been to two different hvac schools.

Edited February 8, 2015 by BryanS

[m_west5]

Manufacturer and model number ?

I would not recommend opening the sealed system until you logically troubleshoot the system first.

Edited February 9, 2015 by Radio Loco

[alamo1718]

The temperature difference across the indoor coil will tell you a lot.

 

Bryan is right, gauge connection is different in heat mode on a heat pump.

 

Sub cool and Super heat are not dependable ways to determine proper charge on heat pumps in the heat mode(low ambient). The only correct method I know is to weigh in the proper charge that is written on the unit.  Then add .6 ounce per foot,  for the length of line set over 15 feet. Then come back in the spring and set it with super heat or sub cooling, depending on your metering device. 

 

 

Heat pumps do not deliver "blazing" hot air into the house. In heat, they actually can feel cool if you stand over the vent and feel it with your hand. The colder is gets outside, the less heat it can bring in from outside. Measure the temp of the air entering the filter and exiting the supply. The best place is actually just before and just after the coil. Don't drill a hole in the coil trying though.

 

The best thing I did when I worked in the apartment industry was to use a infrared temperature gun. Point it at the supply vent and show the customer that it is blowing out hot air. Is it maintaining the temp in the house in cold weather? 

 

In my area, NC, around 30-35 degrees or so the heat pump can't keep up, so it switches to electric. Have you checked the heat strips?