By John West
Chesterfield, Va.

My question involves the use of HH driers. What would be the appropriate decision if all you had on your truck was an HH drier. There is no acid showing in the system, but you use it because that is all you have. Can you safely leave it in the system and why?

From Doug Gildehaus
Product Manager
Sporlan Valve Co.
Washington, Mo.

When the only filter-drier on the truck is an HH style filter-drier, go ahead and install it in the system. The HH types, whether sealed models or replaceable cores, are compatible with common refrigerants and lubricants. They can be installed permanently in a system (provided they are sized properly) since HH types remove water and acid, and filter in the same manner as standard model filter-driers.

In highly contaminated systems, however, HH filter-driers may need to be changed. For larger systems, the HH replaceable core installed in a suction line shell may be replaced with a filter element after system cleanup to reduce pressure drop.

Being selective on when to use the HH style vs. standard models is advantageous. Standard liquid line models are formulated with desiccant mixes that achieve the best balance of water and acid capacities for standard installations.

The HH style includes activated carbon in a desiccant mix. Activated carbon is beneficial in applications when wax-like substances are problematic or for system cleanup (used in suction filter-driers). Since HH types include activated carbon, they have less water capacity than standard filter-driers. Being selective will ensure the best product for the application.


By Bob McLellan
Quartz Hill, Calif.

My questions involve packaged heat pumps ranging from 2.5 tons. On some single-phase models, the manufacturer uses a single-pole contactor (usually on the run winding). I’ve always replaced a worn single-pole contactor with a two-pole contactor.

I’ve been told by other service technicians that if a two-pole is installed, it will break the path of the voltage through the compressor winding (common) which supposedly adds heat to the compressor. I have checked the circuits on units with a one-pole contactor and fail to read any current draw from the unbroken windings S or R. Is this an urban legend or is there any truth here?

From Steven R. Brown
Service Training Specialist
Sidney, Ohio

Obviously, the single-pole will break one leg and the two-pole will break two legs. In either case, the voltage flow is interrupted and there will be no amperage draw. Since there is no amperage flow, no heat buildup will exist in the compressor.

When a single-pole contactor is used, it can open either the hot or the neutral leg. It is best to always break the hot leg. By breaking the hot leg, you will interrupt the voltage.

Let’s think about breaking the neutral leg with a single-pole contactor. If the motor goes to ground, you still have a path for current flow. Voltage is being fed through the hot leg and through the grounded motor to ground. The voltage is not flowing through the contactor.

The fuse or circuit breaker should open. However, if for some reason it doesn’t, you now have potential for an electrical shock. This is why you want to break the hot side of your feed.


By Bill Smith
Allenwood, N.J.

Please explain the difference between bleed and non-bleed thermostatic expansion valves?

How will they affect the starting of a compressor? Can hard start devices be used with either type of valve?

From Steve Esslinger
Senior Applications Engineer
Sporlan Valve Co.
Washington, Mo.

Certain applications utilizing low starting torque single-phase compressor motors (e.g., a permanent split capacitor motor) require some means of pressure equalization during the system off cycle.

Pressure equalization is necessary since low starting torque compressors are not capable of restarting against a large pressure differential.

Typical applications requiring pressure equalization are small air conditioning and heat pump systems which frequently cycle on and off in response to a thermostat.

Bleed ports are designated by the percentage they increase the nominal capacity at a 40 degree evaporator temperature. For example, a 2-ton TEV with a 30 percent bleed will have a capacity of 2.6 tons.

Hard start devices that are applicable for the compressor can be used with either type valve.

The subject of pressure equalization during system off cycle should not be confused with the external equalizer of the TEV. System equalization is accomplished by allowing a certain amount of refrigerant to leak through a machined notch or hole in the valve seat during system off cycle.

The external equalizer of the TEV, however, simply allows the valve to sense evaporator pressure. The external equalizer does not provide pressure equalization during the system off cycle.

Publication date: 02/03/2003