THINGS TO CHECK IF FAN COMES ON WITH LITTLE OR NO HEAT:
Sequencer relays having gone bad are probably the most common reason for this. Each one of the heat strips feeds through these sequencer relays as their control mechanism. If one sequencer or a set of contacts on one fails, then one or more heating strips will not work. Each one of the above pictures is a sequencing relay. A delay occurs before each set of contacts close and a delay before the contacts open again. One in the picture has one set of contacts, another has two, one has three and the other has four sets of contacts. The contact is made through the terminals that are opposite each other on a horizontal plane. Each set is numbered 1 through 5 (if it has that many contacts). The terminals at the bottom are for the 24 VAC control and the stack or stacks above it is a set of contacts. The ones that have three, four or five contacts are actually two or three relays setting beside each other on a common base, but are sequenced so there is a delay after each one makes contact before the others make. You can control a 5 KW heat strip with each set of contacts or control a motor. Sometime it is wired to bring on the first strip AND the fan at the same time on the same contact. Some units will bring in the strips with contactors like this one. This is less common and may require several contactors and they have no delay factor. They are heavier duty, though, and will probably last longer than the sequencer relays. Burned wires can be anywhere and may be the problem. Check for these carefully and repair any that you find. TIP: If a wire in burned at a terminal of a relay, control module or other sensitive locations, chances are the part will have to be replaced. If you replace the wire and not the part, the part may fail later. Burned or broken heat element strips. The heat element wires are a special cadmium/nickel compound and are, of course, isolated from touching anything. 230 VAC is applied to the ends and the wire glows hot --- NOT RED HOT! It doesn't need to be red hot. If enough air flows over it, it will be black hot. Glowing will only occur under the insulators. If these strips are allowed to glow without air flowing over them, they will quickly burn in two. You can buy replacement re-string kits to replace the wire strip and thermal links for just 10 to 13 dollars. You will have to replace the framework also if the insulators are broken and this can get much more expensive. Low air flow will cause the strips to glow too hot and the thermal protectors may be cutting in and out to prevent overheating. Check the filter, grills and fan for airflow problems. Thermostat anticipator setting is too low. Check the section on Thermostats (from the menu at left) for a detailed description of the setting. It may need to be raised to allow longer cycles. Tripped circuit breakers or blown fuses to the supply voltage may be keeping some heat strips out but still allow others and the fan to run normal.