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Low Side Pressure drops to low

Need Cooling on Sun June 02, 2013 11:09 PM User is offline

Year: 2001
Make: dODGE
Model: rAM 2500
Engine Size: 5.9
Refrigerant Type: 134
Ambient Temp: 85
Pressure Low: 35
Pressure High: 195
Country of Origin: United States


The Low side pressure on a Dodge 2500 drops below 25 P.S.I when RPM is increased ;thus the compressor clutch is shut down..

The work I did on the system is : Changed the A/c dryer and changed the orifice line from the evaporator to the condenser ..

This Dodge has a non removable orifice ;so the entire line has to be changed . evacuated the system and recharged to the recommended amount of Freon R- 134 32o/z

At idle the compressor will stay running /clutch will be engaged ..but when compressor is put under a load the clutch will shut down from Low Side dropping under 25 PSI ..

High side when compressor is engaged is 195 /Temp @ 85 F

Any help much appreciated ..

Thanks in Advance

mk378 on Sun June 02, 2013 11:53 PM User is offline

The pressures seem OK. Something should be getting cold. The evaporator and suction line don't get cold at all?

Need Cooling on Mon June 03, 2013 1:01 AM User is offline

Hello mk 378

Yes, suction line does get cold ..but after about 10 minutes of driving the Compressor clutch will not engage ..the low side is too low ..

and the truck cabin is still warm ......also the amount of Freon is correct @32o/z ..

While having the gauges connected to the system and increasing the RPM's to approx 1400 RPM the clutch will kick out /disengage ....

The lowside drops below the cutoff for the lowside switch @25 PSI ....

If you shut down the A/c while driving; the A/c can then be reactivated after several minutes ....

TIA ..

Edited: Mon June 03, 2013 at 1:03 AM by Need Cooling

Dougflas on Mon June 03, 2013 5:11 AM User is offline

Sounds like the cycling switch if one is used. Also, may be slightly low on R134.

mk378 on Mon June 03, 2013 9:41 AM User is offline

Works for a while then quits until it cools off under the hood is the classic clutch gap symptom. Also suspect the switch.

Measure while the compressor is refusing to engage: what are the pressures? Is voltage being applied to the clutch coil?

MrBillPro on Mon June 03, 2013 9:54 AM User is offlineView users profile

Adj. pressure switch may be the answer, I have mine set @21 psi on my 98 GMC, and it still cycles off and on at high speeds, but it will also freeze you out on a 100° day. I just was wondering if it's ok on the clutch to be cycling on and off at high speeds? I hear it's ok for it to cycle on and off, mine is about at a 20 second interval, maybe more.

Don't take life seriously... Its not permanent.

Edited: Mon June 03, 2013 at 9:55 AM by MrBillPro

Need Cooling on Mon June 03, 2013 12:15 PM User is offline

@ mk 378

Thanks.... I'll take a look at the clutch gap.... compressor is a Sanden model U4833..

Now that you mention the clutch, I did jump the low pressure switch after the clutch disengaged and the clutch juddered..

The clutch moved slightly then stopped ...The clutch moved approx 1/8 of a revolution ...

I removed my jumper immediately...I didn't t want to do any damage to the compressor ....

"Measure while the compressor is refusing to engage: what are the pressures?'

Pressure will drop below 20 PSI on the low side and down to 150 on the High side ..

The compressor will cycle at this point but engine temp is still relatively cool but after approx 10 minutes of driving

the compressor clutch will not engage...

"Also suspect the switch."

Which switch are you referring to?

I have to check but I believe this model does have a 'Pressure Transducer' switch in the high side

This switch feeds information to the PCM with regard to system pressure and cycles the clutch ...


Need Cooling on Wed June 05, 2013 11:51 AM User is offline

@mk 378 I took a look at the clutch gap and it's very close to the pulley...15/31 thousands of an inch is spec.

I need shims to increase the 'air gap'; where would purchase the shims ?

I have the tools to pull the clutch ..I have a master cool tool kit, that covers several compressors ...

I did a Goggle search and didn't come up with an answer with regard to the shims ..

Thanks in Advance ...

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