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Short cycling but not low on 134a

Mopar4u on Sat June 07, 2014 8:09 AM User is offline

Year: 1999
Make: Dodge
Model: Neon
Engine Size: 2.0
Refrigerant Type: 134a
Ambient Temp: 84
Pressure Low: 25-40
Pressure High: 250-350
Country of Origin: United States

Getting this a/c going as i bought it from previous owner not working. I replaced the condenser, pulled a 30 minute vacuum, put in 28oz of 134a. With the above credentials I'm getting 43-45 deg at the center vent on max. The problem I'm seeing is the compressor is cycling about every 5 seconds. I added another 4oz because I thought typically short cycling is related to low 134a. Adding the 4oz didn't change anything. Not sure where to go from here and am looking for advice.

mk378 on Sat June 07, 2014 8:34 AM User is offline

This is a TXV system. In normal operation, there is no pressure-activated cycling like a CCOT, instead it cycles on evaporator temperature. Cycling is good, it means the evaporator is cold. You are done. Close the hood and walk away with fingers crossed...

Mopar4u on Sat June 07, 2014 8:51 AM User is offline

It does have a low and high pressure switch in the system. I thought these control the cycling?

webbch on Sat June 07, 2014 9:15 AM User is offlineView users profile

What prompted you to replace the condenser? Just trying to get an idea of the original problem/diagnosis/repair that took place. The vents aren't too far off from where they should be - maybe clamp off a heater hose line to see if you're getting a little bit of re-heating. However, pushing a high side pressure of 350 psi at only 84 ambient seems a bit high to me. Is that the point at which the compressor cycles off?

Mopar4u on Sat June 07, 2014 9:23 AM User is offline

I replaced it because when I filled it with 134a (the first time) it sprung a huge hole in the corner of the original condenser and 134a sprayed out. Must have rusted out.

Yes that is the max reading then cycle turns off.

I'm not saying this isn't normal operation, I just don't know.

webbch on Sat June 07, 2014 11:07 AM User is offlineView users profile

Even though the high side pressure seems a bit high to me, it's unlikely that the HPCO switch is shutting you down - those are set to shut off at 450 psi, and re-engage at 360. More likely what mk378 said that the evap temp sensor (at the low pressure of 25 psi) gets the evaporator cold enough to shut off the compressor.

You _might_ have a slight blockage in the TXV...potentially from rust particles from the previously rusted out condenser, but it's hard to say at this point, as the symptoms aren't too strong yet.

Since your vents are a little warmer than you'd like, I'd still recommend clamping off the supply line to the heater core to rule out a re-heating issue. Heater control valves are notorious for not fully shutting off the flow of hot water to the heater core, which defeats the work done by the a/c system. Other than that, the performance doesn't look all that bad at about a 40 deg drop in temperature on a relatively cool day (Yes, as an Arizonan, I consider 84 to be "relatively cool")

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