Japanese electronics conglomerate Mitsubishi Electric Corp. admitted Tuesday to problems regarding its inspections of air conditioners for train carriages, with sources familiar with the matter alleging data fabrication possibly spanning more than 30 years.

While asserting that safety has not been compromised, the company admitted to inspection failures and suspended shipments of affected products to train operators. It has also reported the matter to the Ministry of Economy, Trade and Industry.

Mitsubishi Electric, which produces a wide range of products from home appliances to heavy machinery and defense equipment, has been hit by quality control failures for items such as semiconductors and electric devices in recent years.

According to the sources, the air conditioners are manufactured at the company's plant in Nagasaki Prefecture, southwestern Japan. The plant is also in charge of product inspections.

But inspection failures are believed to have started around 1985 or earlier, the sources said.

Mitsubishi Electric was supposed to conduct customer-tailored inspections on the products, but the company has failed to do so.

At a general shareholders meeting on Tuesday, Mitsubishi Electric did not explain the issue. That night, however, the Tokyo-based company issued a statement saying it is investigating the matter as an in-house probe in mid-June revealed inappropriate inspection practices.

The company said it will address the matter promptly and announce the findings.

Mitsubishi Electric ships air conditioners for various train carriages at home and abroad, including Japanese bullet trains, according to its official website.

The company touts a high market share in train air-conditioning systems as a result of its providing maintenance services as a manufacturer.