Here is a communication I had with customer support on the Parrallax 7100 converter in our trailer. Although our converter was not continually running it would cycle on and off every few seconds. If nothing else this will give you a contact at Parrallax.
From: Marty Redd <email@example.com>
Subject: RE: Model 7100 Question
Date: Tuesday, October 20, 2009, 8:16 AM
The fan circuit in the 7155 is micro processor controlled and the fan is cycled on and off determined by:
1. Primarily - the amount of DC amperage the converter section is supplying to the 12 volt system.
2. Secondarily - the ambient temperature of the mounting location where the converter is mounted and how much access is available for conditioned room air.
A basic test for normal operation of the fan circuit would be as follows:
1. Disconnect the "house" batteries.
2. Temperature inside the RV must be 70 degrees F or higher.
3. Converter power must be on.
4. Turn on approximately 1/2 of the 12 volt lights in the RV.
The idea here is to get the converter to a DC load amperage of 30- 40 amps of output. You may take the load to 50-55 amps if you have the capacity to measure the DC current load, but you must not go over 55 amperes of DC load.
5. Let this load operate for 10-15 minutes. After this time frame the fan should be on constantly at full speed and not cycling.
6. If the converter fan circuit passes this test, the fan circuit is operating normally.
RV Technical Support and Training
Parallax Power Supply
A Division of Connecticut-Electric, Inc.
Ph: 800-443-4859 ext 305
Direct Ph/Fax 866-806-1541