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Relay

Relay

# HVAC Relays - Start, Potential, Control & Fan Relays

Shop replacement relays for air conditioning systems, heat pumps, and HVAC equipment. We stock start relays, potential relays, control relays, fan relays, and time delay relays from all major brands at our Westland, Michigan warehouse.

## Why Buy Relays From Technical Hot & Cold?

**Complete Relay Selection**
From simple start relays to complex control relays, we stock the switching devices your HVAC system needs.

**Quality Brands**
Supco, Mars, Packard, White-Rodgers, Honeywell - trusted names in HVAC relays and controls.

**Same-Day Shipping**
Relays in stock ship today when ordered before 3PM EST from our Westland warehouse.

**Expert Application Support**
Relays have specific electrical ratings. Our team helps ensure you get the correct relay for your application.

## Types of HVAC Relays

### Start Relays (Current Relays)
Help single-phase compressors start.

**Function:**
- Energize start winding briefly
- Disconnect after motor reaches speed
- Current-operated switching
- Used with start capacitors

**How They Work:**
- High inrush current closes relay
- Start capacitor energized
- Motor reaches 75% speed
- Current drops, relay opens
- Start capacitor disconnected

**Applications:**
- Residential AC compressors
- Refrigeration compressors
- Single-phase motors
- Hard-to-start systems

**Common Issues:**
- Compressor won't start
- Hums but doesn't run
- Trips breaker
- Relay clicking

### Potential Relays (Voltage Relays)
Disconnect start capacitor based on back-EMF.

**Function:**
- Monitor motor speed via voltage
- Energize start winding initially
- Disconnect when motor at speed
- Voltage-operated switching

**How They Work:**
- Start: relay closed, start cap in circuit
- Motor speeds up
- Back-EMF voltage rises
- Relay opens at pickup voltage
- Start capacitor disconnected

**Applications:**
- Larger compressors (3+ HP)
- Commercial AC systems
- High-starting-torque motors
- Permanent split capacitor (PSC) motors

**Specifications:**
- Pickup voltage (when relay opens)
- Dropout voltage (when relay closes)
- Must match motor characteristics

### Control Relays (General Purpose)
Switch circuits on/off based on control signal.

**Function:**
- Remote switching
- Multiple contact sets
- Isolate control from load
- Amplify small signals

**Applications:**
- Energize contactors
- Switch fan motors
- Control multiple circuits
- Interlock circuits
- Sequence operations

**Configurations:**
- SPST (single pole, single throw)
- SPDT (single pole, double throw)
- DPDT (double pole, double throw)
- Multiple poles available

**Coil Voltages:**
- 24V AC (most common in HVAC)
- 120V AC
- 240V AC
- 12V DC, 24V DC (controls)

### Fan Relays
Control fan operation independently.

**Function:**
- Turn fan on/off
- Independent of thermostat G wire
- Time-delay available
- Override controls

**Applications:**
- Continuous fan operation
- Ventilation systems
- Air quality equipment
- Dehumidification cycles

**Types:**
- Simple on/off relay
- Time-delay relay (fan runs after cooling)
- Adjustable delay
- Multiple outputs

### Time Delay Relays
Provide timed switching operations.

**Function:**
- Delay on make (delay before energizing)
- Delay on break (delay before de-energizing)
- Interval timing
- Repeat cycle timing

**Applications:**
- Compressor short-cycle prevention
- Fan delays (run-on after cooling)
- Defrost cycles
- Staging equipment
- Pump-down cycles

**Adjustment:**
- Fixed time (non-adjustable)
- Adjustable (dial or DIP switches)
- 30 seconds to 10+ minutes typical

## Popular Relay Brands

**Aftermarket Manufacturers:**
- **Supco** - Quality replacement relays
- **Mars** - Reliable HVAC relays
- **Packard** - Complete relay line
- **White-Rodgers** - Control relays
- **Honeywell** - Control relays
- **ICM Controls** - Universal relays

**OEM Brands:**
- **Carrier/Bryant** - OEM relays
- **Trane** - OEM relays
- **Lennox** - OEM relays
- **Goodman** - OEM relays

## How to Select the Right Relay

### For Start Relays:

**Information Needed:**
1. **Compressor amperage** - RLA or FLA
2. **Motor type** - PSC or CSIR
3. **Start capacitor** - If used
4. **Relay mounting** - Orientation

**Selection:**
- Match amperage rating
- Verify mounting compatibility
- Check terminal configuration

### For Potential Relays:

**Information Needed:**
1. **Pickup voltage** - Usually on old relay
2. **Dropout voltage** - Usually on old relay
3. **Contact rating** - Amps
4. **Continuous coil rating** - Important!

**Critical:**
- Must match pickup/dropout voltages
- Wrong voltage = improper operation
- Consult compressor/motor data

### For Control Relays:

**Information Needed:**
1. **Coil voltage** - 24V, 120V, 240V
2. **Contact configuration** - SPST, SPDT, DPDT
3. **Contact rating** - Amps load
4. **Mounting type** - Socket, base, DIN rail

## Relay Troubleshooting

### Start Relay Problems:

**Compressor Won't Start:**
- Relay contacts stuck open
- Relay coil failed
- Wrong relay for application
- Wiring problems

**Compressor Hums:**
- Relay not closing
- Start capacitor failed
- Bad compressor
- Low voltage

**Relay Clicks Rapidly:**
- Short cycling
- Low voltage
- Compressor overload
- Bad relay

**Testing Start Relay:**
1. Power off, remove relay
2. Test continuity across contacts
3. Should be closed (normally closed type)
4. Or open (normally open type)
5. Shake gently - should hear click
6. Replace if suspect

### Potential Relay Problems:

**Compressor Tries to Start but Fails:**
- Relay not closing initially
- Start capacitor not energized
- Bad relay coil
- Wrong pickup voltage

**Start Capacitor Stays in Circuit:**
- Relay won't open
- Wrong pickup voltage (too high)
- Bad relay
- Capacitor will overheat and fail

**Testing Potential Relay:**
1. Power off
2. Measure coil resistance (should be ~10-50 ohms)
3. Test contacts (should be closed at rest)
4. Apply rated voltage to coil
5. Contacts should open
6. Remove voltage, contacts should close

### Control Relay Problems:

**Relay Won't Energize:**
- No voltage to coil
- Bad coil
- Blown fuse
- Wiring problem

**Contacts Won't Close:**
- Stuck mechanism
- Burned contacts
- Weak coil
- Wrong voltage

**Contacts Welded Closed:**
- Overload
- Contact arcing
- Wrong contact rating
- Replace relay

**Testing Control Relay:**
1. Power off
2. Measure coil resistance
3. Apply rated voltage to coil
4. Should hear/feel click
5. Test continuity across contacts
6. Should close when energized

## Relay Installation

**Safety First:**
1. Turn off all power
2. Verify no voltage
3. Discharge capacitors
4. Use proper tools

**General Installation:**

1. **Remove Old Relay**
   - Photo wiring first
   - Label all wires
   - Note orientation
   - Remove mounting hardware

2. **Compare New to Old**
   - Match terminal configuration
   - Verify electrical ratings
   - Check physical size
   - Confirm mounting type

3. **Install New Relay**
   - Proper orientation (important!)
   - Secure mounting
   - Ensure good contact with terminals

4. **Connect Wiring**
   - Match wire positions
   - Secure all connections
   - No bare wire exposed
   - Double-check against photos

5. **Test Operation**
   - Restore power
   - Operate system
   - Listen for relay click
   - Monitor several cycles
   - Check for overheating

## Relay Orientation

**Critical for Some Relays:**

**Start Relays:**
- Must be mounted correctly
- Usually vertical orientation
- Arrow indicates direction
- Wrong orientation = won't work

**Potential Relays:**
- Orientation usually not critical
- Follow manufacturer guidelines
- Secure mounting important

**Control Relays:**
- Usually orientation-independent
- Socket-mount type may have requirements
- Check documentation

## Common Installation Mistakes

❌ **Wrong Relay Type**
- Start relay vs potential relay
- Different functions
- Won't work correctly

❌ **Wrong Electrical Rating**
- Contact amperage too low
- Coil voltage mismatch
- Pickup voltage wrong (potential relay)

❌ **Poor Mounting**
- Loose mounting
- Wrong orientation
- Vibration can cause failure

❌ **Wiring Errors**
- Wrong terminals
- Reversed connections
- Loose connections

## Relay Maintenance

**Inspection:**
- Annual inspection
- Check for overheating
- Listen for proper operation
- Verify secure mounting

**Replace If:**
- Contacts pitted or burned
- Coil overheating
- Intermittent operation
- Age/wear (10+ years)

**Preventive:**
- Replace during compressor replacement
- Replace with contactor
- Stock common types

## Relay FAQs

**Q: What's the difference between start relay and potential relay?**
A: 
- **Start relay**: Current-operated, for smaller compressors
- **Potential relay**: Voltage-operated, for larger compressors
- Different sensing methods for same goal

**Q: Can I bypass the relay to test?**
A: Briefly for diagnosis only, never permanent. Can damage compressor without proper start assistance.

**Q: Why does my relay click rapidly?**
A: Indicates:
- Short cycling protection
- Low voltage
- Compressor overload
- Bad relay or capacitor

**Q: How do I know which type of relay I need?**
A: Check:
- Old relay part number
- Compressor specifications
- System wiring diagram
- Usually labeled on compressor

**Q: Can I use a start relay instead of potential relay?**
A: No. Different operating principles. Must use correct type for application.

**Q: Why did my new relay fail quickly?**
A: Usually indicates:
- Wrong relay for application
- Compressor problems
- Bad start capacitor
- Voltage issues

**Q: How long do relays last?**
A: 
- Start/potential relays: 10-15 years typical
- Control relays: 100,000+ operations
- Depends on usage and conditions

**Q: Can relays be repaired?**
A: Generally no. Contacts cannot be replaced economically. Replace failed relays.

## For HVAC Contractors

**Stock Common Types:**
- Universal start relays
- Common potential relay voltages
- 24V control relays (SPDT most useful)
- Time delay relays

**Diagnostic Tools:**
- Multimeter for testing
- Voltage/amp clamp meter
- Relay tester (optional)

## Need Help Selecting a Relay?

Our HVAC parts specialists are here to help! Contact us:
- **Phone:** [Your phone number]
- **Email:** [Your email]
- **Hours:** [Your business hours]
- **Location:** Westland, MI - Local pickup available

**Have your compressor specifications or old relay part number ready for exact match!**

Can't find what you're looking for?

If you don't see your model or part, call us! Our friendly technicians are standing by. We can help you find the part you need with guaranteed fitment. Speak with us today at (734) 326-3900.

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