What is the relay number for the Passat B5 compressor?

[LeLyla]

Passat relay is No. 100. Here is more information about the relay: 1. Concept: Relay (English name: relay) is an electrical control device that causes a predetermined step change in the controlled quantity in the electrical output circuit when the change of the input quantity (excitation quantity) reaches the specified requirements. 2. Function: It has an interactive relationship between the control system (also known as the input circuit) and the controlled system (also known as the output circuit). It is usually used in automatic control circuits, and it is actually an "automatic switch" that uses small current to control large current operation. Therefore, it plays a role in automatic adjustment, safety protection, circuit conversion, etc. in the circuit.

[Reid]

The compressor relay number for the Passat B5 is typically 100 or 109, located in the relay box in the engine compartment. For the B5 model, Volkswagen often uses a relay with a numbered label to control the air conditioning compressor circuit. After opening the fuse box cover, you can find the corresponding label. If the air conditioning suddenly stops working and the fan doesn't respond, it might be due to a faulty relay. A damaged relay can prevent the compressor from starting, leading to poor cooling performance. During inspection, first turn off the engine, remove the relay, and check for any burnt or loose contacts. It's recommended to regularly clean the relay box to avoid dust buildup and pay attention to any unusual noises from the air conditioning while driving. If experienced, you can use a multimeter to test the relay's continuity and ensure proper power supply. When replacing, choose a model that matches the original factory specifications to avoid compatibility issues. If unsure about the relay number, refer to your vehicle manual or search online forums where owners share specific diagrams.

[VonFelicity]

Speaking of the Passat B5's air conditioning issues, I recall that the relay number often encountered during repairs is position 100. Having driven for many years, I've replaced the relay several times myself. The compressor relay controls the AC cooling—if it fails, driving in summer can be unbearable. It's usually located on the right side of the fuse box, and you can spot the small square relay with a label when you open the cover. If the AC doesn’t start or the compressor makes a clicking noise, this part should be checked first. A burnt-out relay is a common issue, especially after prolonged vibration loosens the contacts. Replacing it is straightforward: just pull out the old relay and install a new one of the same model—it’s inexpensive. I recommend keeping a spare on hand and checking it before long trips. Also, keeping the cabin clean can reduce relay failures, such as avoiding moisture or grease entering the box. The Passat’s AC system isn’t overly complex, but don’t overlook this small relay—it’s crucial for the entire cooling cycle’s safety. If you can’t find the number, take a photo and show it to a mechanic.

[SanClaire]

The Passat B5 compressor relay number may vary across different model years, commonly labeled as 109 or 100 in the relay box. When activating the air conditioning system, the relay controls current flow—if the compressor fails to operate, the relay becomes the primary troubleshooting focus. During inspection, open the hood and locate the numbering chart on the back of the fuse box cover to match the compressor entry. A properly functioning relay should emit a faint clicking sound. If the relay fails, the AC will lose cooling capability. Basic maintenance involves cleaning contact points from dust to prevent overheating damage. Replacement relays must match the original model—genuine VW parts are recommended. Avoid prolonged high-pressure AC operation to extend lifespan. If the number is unclear, consult the vehicle manual or online databases.