2nd Gen Non-Engine/Transmission A/C Compressor Cycles

[turretplug]

Is the A/C compressor supposed to cycle on and off every four seconds. When I observe mine looking down from the front that is the cycle that it seems to follow. My truck has been doing this for a long time when the engine is at idle. I do not know if this cycle continues as I am driving.

 

[Vaughn MacKenzie]

It will as long as the selector is set for defrost, AC, or blend (the icon with air from the vents and floor).

 

[fest3er]

Is the A/C compressor supposed to cycle on and off every four seconds. When I observe mine looking down from the front that is the cycle that it seems to follow. My truck has been doing this for a long time when the engine is at idle. I do not know if this cycle continues as I am driving.

It's probably telling you it's low on R134A or the low pressure switch needs cleaning or replacing. The compressor is sucking the low pressure side down to less than 25 PSI rapidly, and the low pressure switch opens.



Remove the low pressure switch from the dryer/accumulator and clean it out with carb cleaner. And make sure it's all evaporated before reinstalling it. If that doesn't make a difference, you probably need about a half can of R143A.



If it's running well, it should cycle about every minute or three. On mine, I have to add enough so that it stops cycling before I get enough cooling. I think that tells me the evaporator is clogged with dust and mold. (Well, it did until the leak in the evap grew too large. I still haven't replaced it yet. )

 

[WestTN]

It IS telling you that it id low on freon.

 

[Crowhurst]

The Chrysler 1998 12v shop manual at page 24-12 states that ten or more cycles per minute indicates a fault. Assuming a cycle is "on and off", then 4 seconds on and 4 seconds off is above the minimum for a properly working system. I just checked mine, and it's 5 seconds on and then 5 seconds off at idle when first switched on. If it comes on for 3 seconds or less, (10 cycles per minute) the manual gives as possible causes:

1. Low refrigerant system charge.

2. Faulty low pressure cycling switch.

3. Faulty Power Control Module.

I hope this helps.

Nick.

 

[turretplug]

Since I posted I have added add some R134a. The hose I borrowed did not have a pressure gauge. I now have a refill hose with the gauge. What PSI should the gauge read when the system is full. I want to eliminate refrigerant as the problem. This is the first problem I have posted and I want to thank all of the members for their input.

 

[fest3er]

Since I posted I have added add some R134a. The hose I borrowed did not have a pressure gauge. I now have a refill hose with the gauge. What PSI should the gauge read when the system is full. I want to eliminate refrigerant as the problem. This is the first problem I have posted and I want to thank all of the members for their input.

While the system is off, pressure readings are meaningless. During operation, the low-pressure-side pressure should range between about 25 PSI to about 43 PSI.



When the compressor is running, it pulls r134 out of the low pressure side, reducing the pressure there. If the pressure drops below about 25 PSI, the low pressure switch opens and disables the compressor. Now the high pressure side continues to expand and evaporate, cooling the cab and pushing r134 back into the low pressure side. When the low pressure side rises to about 43 PSI, the low pressure switch should close and re-engage the clutch.



Apparently, the ideal amount of r134 in the system is that which maximizes compressor cycling while still producing the specified temp in the A/C duct outlet. I've never found that to work over 90F, or 80F with very high humidity.

 

[ata]

Ambient air temp (out side air) has a lot to do with the low side psi. At 70 deg. the low side psi should be 25 to 35 psi at 80 degs. 32 to 40 psi at 90 degs. 37 to 45 psi 100 degs. 39 to 50 psi at 110 degs. 45 to 55 psi. These are the numbers for the Dodge r134 system. Do Not over charge the low side of the system.