1979-1980 Dodge D300 A/C Clutch Cycle Switch Replacement Guide
If your D300's air conditioning is blowing warm or not working at all, a faulty A/C clutch cycle switch could be the culprit.
- A faulty A/C clutch cycle switch is a common cause for A/C failure on a 1979-1980 D300.
- Symptoms include warm air, the compressor not turning on, or rapid on/off cycling.
- Aftermarket parts from brands like Four Seasons are the only practical replacement option, as OEM parts are no longer available.
- Replacement is simple for a DIYer and does not require discharging the A/C system.
Is Your D300's A/C Ready for the Heat?
For owners of a classic 1979-1980 Dodge D300, keeping the factory air conditioning running is a common goal. When the A/C starts blowing warm or stops working entirely, many suspect a major, expensive failure. However, a small and relatively inexpensive part called the A/C clutch cycle switch is often the cause. This switch is one of the most common failure points in an older A/C system due to the constant wear on its internal electrical contacts.
Symptoms of a Failing A/C Clutch Cycle Switch
A bad A/C clutch cycle switch will produce a few distinct symptoms. Paying attention to these signs can help you diagnose the problem quickly.
- A/C Blows Warm or Not as Cold: If the switch is failing, it may not allow the system to pressurize correctly, resulting in poor cooling performance.
- A/C Does Not Work at All: A completely failed switch will not send the signal to engage the compressor's clutch, meaning the A/C system won't produce any cold air.
- Compressor Clutch Doesn't Engage: If you turn on the A/C and the center part of the compressor pulley doesn't start spinning, the cycling switch could be the reason.
- A/C Compressor Cycles On and Off Rapidly: A faulty switch can send erratic signals, causing the compressor to click on and off too frequently. This can sometimes be heard as a clicking noise from the engine bay.
A Note on Refrigerant
Your 1979-1980 D300 was originally equipped with an R12 refrigerant system. Many of these trucks have since been converted to use modern R134a refrigerant. The symptoms of a bad cycling switch can be identical to those of a system that is simply low on refrigerant. Before replacing the switch, it's a good idea to have the system pressure checked by a professional to rule out a leak.
Choosing an Aftermarket A/C Clutch Cycle Switch
For a vehicle of this age, finding a new original equipment (OEM) A/C clutch cycle switch from Mopar is highly unlikely. The aftermarket is the primary source for these parts, keeping classic trucks like the D300 on the road.
Brand Spotlight: Four Seasons
Four Seasons is a well-established brand in the automotive A/C parts industry. They are a common and reliable choice for components like switches, compressors, and other A/C system parts. For the 1979-1980 D300, the Four Seasons switch is a direct-fit replacement designed to meet original specifications. Given the scarcity of OEM parts, a quality aftermarket brand like Four Seasons is a dependable option for this repair.
| Part Type | Estimated Cost |
|---|---|
| New Aftermarket (Four Seasons) | $38.72 |
| Shop Labor | $50 - $100 |
DIY Replacement is Simple
Replacing the A/C clutch cycle switch is a straightforward job for a DIYer. It's typically located on the A/C accumulator (a metal can-like component on the low-pressure side of the system). The switch is mounted on a Schrader valve, similar to a tire valve, so you can unscrew the old one and install the new one without losing refrigerant. Simply disconnect the electrical connector, unscrew the old switch with a wrench, and install the new one.
Frequently Asked Questions
Do I need to drain the refrigerant to replace the A/C clutch cycle switch?
No. On most vehicles, including the Dodge D300, the switch is mounted on a Schrader valve that automatically seals the system when the switch is removed. You can replace it without evacuating the refrigerant.
Where is the A/C clutch cycle switch located on my D300?
It is usually found screwed into the A/C accumulator, which is a metal cylinder located on the low-pressure side of the A/C system, often near the firewall on the passenger side of the engine bay.
Could my A/C problem just be a blown fuse?
Yes, it's possible. Before replacing parts, it's always a good idea to check the A/C fuse in the vehicle's fuse box to make sure it hasn't blown.
Will a new switch fix my A/C if it has been converted to R134a?
Yes. The aftermarket Four Seasons switch is compatible with both the original R12 and converted R134a systems. The switch's function is to react to pressure, which it does regardless of the specific refrigerant type.
Were there any recalls for the A/C system on the 1979-1980 Dodge D300?
Searches of the NHTSA database did not find any recalls specifically for the A/C clutch cycle switch. However, a recall was issued for some 1979 Dodge trucks because condensate water could accumulate in the A/C blower housing, potentially causing the blower motor to fail. This is a separate issue from the cycling switch.
Technical Specifications
The Four Seasons 35720 is a system-mounted, preset cycling temperature switch with a mechanical design and OE-style connectors.
We Have This Part in Stock
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.