Heating - Flow of Heat From Heater Core Fluctuates: Overview

90saab02

FILE IN VOL.

S.I. Man. I
SEC. PG.

A-8 120
Subject: Circulation Pump For The Heater System Issue: 03/90-1221

Application: 1985-89 900 Models


On certain cars with plastic heater control valves, the flow of heat from the heater core may fluctuate, depending on driving conditions. These heater control valves have a constant by-pass flow and the heater core may not receive sufficient coolant flow at low engine RPM to provide a constant, comfortable level of heat during certain situations, such as extensive stop-and-go driving in cold weather.

To remedy a persistent complaint about this problem a circulation pump may be installed. The pump starts when the ignition is turned on and supplies the heater control valve and the heater core with a constant flow of coolant which in turn means that the passenger compartment temperature is not dependent on engine RPM.

Before installing a circulation pump, investigate and remedy all other potential sources of insufficient heat output such as a blocked heater core, faulty thermostat, etc.


NOTE

This kit will not remedy complaints of insufficient heat during highway driving, or driving conditions other than extensive idling and stop-and-go traffic. There is sufficient coolant flow through the heater core at any engine speed above approximately 1500 rpm and the circulation pump will not improve a complaint of poor heat at engine speeds above this level. This kit is not intended for 1990 models equipped with ABS.