7.02-1B: Mercoid 1930 Automatic Temperature Control

HHCC Accession No. 2006.029HHCC Classification Code: 7.02-1B

An early, commercial application, hydraulic bellows actuated, ambient temperature sensing, automatic temperature control; equipped with line voltage, tilting mercury tube switch and unusual rotary quick-make-and-break, manual on-off switch, for use in small food store, walk-in-refrigerators, Mercoid, 1930.

One of a matched set of similar Mercoid, early refrigeration system controllers, profiling a range of temperature/pressure control applications met by this pioneering manufacture, employing various design modifications made to same basic configuration [See items ID # 153- 155].

Image Gallery (2 Images)

7.02 Refrigerating and Air Conditioning Pressure and Temperature Controls - Commercial


Mercoid, American Radiator Company


Mercoid Control, American Radiator Company, USA [See note#1]



Serial No.:



6 x 3 x 9’ high


5 lbs.




Exhibit, education, and research quality, illustrating a significant milestone in the evolution of early FHP, small commercial refrigeration system controls, employing hydraulic bellows actuators.

Patent Date/Number:

From York County (York Region) Ontario, once a rich agricultural hinterlands, attracting early settlement in the last years of the 18th century. Located on the north slopes of the Oak Ridges Moraine, within 20 miles of Toronto, the County would also attract early ex-urban development, to be come a wealthy market place for the emerging household and consumer technologies of the early and mid 20th century.

This artifact was discovered in the 1950’s in the used stock of T. H. Oliver, Refrigeration and Electric Sales and Service, Aurora, Ontario, an early worker in the field of agricultural, industrial and consumer technology.

Type and Design:

hydraulic bellows actuated, ambient air temperature, sensing unit in copper
tilting mercury tube switching


heavy steel, plated enclosure

Special Features:

Of special interest is the glass enclosed, mercury bulb switch, still in tact and operable. These are immensely fragile devices by definition and seldom have a long life, particularly after being taken out of service.
Unusual Danfield rotary quick-make-and-break, snop action, manual on-off switch, HEPC approved, with white porcelain base and black Bakelite cover and control knob,with handsome corporate logo. Smith and Stone, with facilities in George town Ontario, 5 amp conduit fitting base for rotary switch
Large electrical junction box with 4 electrical connector knock-outs, representative of the wiring practice approved for commercial equipment of the period, which required heavy steel shielded twin conductor cable referred to as BX.

Performance Characteristics:
Control and Regulation:
Targeted Market Segment:
Consumer Acceptance:
Market Price:
Technological Significance:

An exemplar of what is likely the first generation of wide spread, commercially manufactured and marketed pressure and temperature refrigeration controllers, popularly found in Canada.

The control, designed to mounted inside the refrigerated space, sensed the temperature through a copper sheathed bellows mechanism. A line voltage, manual on-off switch was attached for convenience. The rotary quick-make-and-break style was popular in the period, being extensively used on electrical stoves

The electrical switching properties of mercury had been discovered and the tilting mercury bulb would become the switching method of choice for much of the early 20th century for fractional HP applications. It was a period in which little empirical design data was available on alternating current switching. With an induction motor rating of up to 1 HP, and a split-phase rating of ‘ HP this controller and most like it of the period was limited to fractional HP applications.

One of a matched set of similar Mercoid, early refrigeration system controllers, profiling a range of temperature/pressure control applications met by this pioneering manufacture, employing design modifications made to this basic configuration. This economic, robust configuration provided a platform readily adaptable to a wide range of commercial refrigeration field requirements [See items ID # 153- 155].

Industrial Significance:

A range of corporate names appear on the controls in the series, suggesting a range of corporate partnerships between Mercoid and other early players in the refrigeration control field: American Radiator Company; The Federal Gauge Company; Detroit Lubricator Company. The genre would give way within the decade to smaller, more sophisticated engineering approaches, yielding increasingly more precise refrigeration system control [See ID # 163 to 165].

Socio-economic Significance:

This generation of pioneering work in commercial refrigeration applications of FHP, automatic control engineering, with all its limitations, none the less enabled the first generation of commercial refrigerated appliances to hit the market. Included were ‘reach-in-refrigerators’, ‘walk-in-refrigerators’ and refrigerated display cases that would soon appear in the local food market [See note 2]. The life of Canadians was about to change dramatically, with a range of fresh foods and new taste delights to be experienced - year around.

It was a period devoid of the large, chain food stores, of the late 20th and early 21st century. These would have to await the development of subsequent generations of food store refrigeration equipment, which were still several decades away. In the interim the small, often family run, store would flourish, supported by this new 20th century refrigeration equipment and automatic control technology

The commercial reach-in refrigerator designed for small food store applications was an adaptation of the household cabinet refrigerator, larger in size and with greater horsepower. However, the small commercial walk-in refrigerator was a new, exciting innovation of the period.

Here-to-for entire refrigerated rooms appeared in refrigerated warehouse facilities only, operated by high-pressure ammonia refrigeration compressors. With the development of small FHP systems and the availability of low-pressure refrigerants that would all quickly change. Meticulously constructed with wooden framing and tar coated, natural cork panels, they would be the marvel of the day. [See classification 8.02 for samples of natural cork insulation]

Socio-cultural Significance:
  • See above

G. Leslie Oliver, The T. H. Oliver HVACR Collection

HHCC Storage Location:
Bibliographic References:
  1. A Google Search of Mercoid, Jan. 2005 indicates that the company name is still associated with the field, now as a division of the Dwyer Instruments Inc. Michigan City Ind.
  2. for images of early commercial refrigerated appliances see Kelvinator and Frigidaire applications manuals

Related posts