I have a 1994 Dodge ram van B350 that was converted into a camper van by Roadtrek. I have this very odd A/C issue and would appreciate any input. So, it all started when I tried to find an ignition wire for a new electric radiator fan I was installing. I thought I had found one and tapped into it, but it apparently went to my AC system somewhere when I traced it. Almost immediately upon having the fan installed with the tapped line and turning the A/C on, the high pressure connection to my compressor completely exploded, the o ring bent open, and I lost all my freon in 10 seconds in a huge cloud of smoke...

So then I got a new o ring and got the high pressure line to sit again and recharged it. Everything seemed fine and was working but now there's three weird things going on. First, the compressor is making a very loud rattling sound that only gets worse when accelerating. Second, at high speeds like 65 mph, the AC clutch disengages and engages rapidly and I completely loose horsepower, but the ac air gets like 100 times colder. The AC clutch almost acts like a brake at that speed. Third, the sight glass bubbles like crazy and makes a loud hissing sound. Also, I want to mention it's been converted from R-12 to R134-A

I understand I may have fried my whole A/C system, but any thoughts would be appreciated.

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    Welcome to Motor Vehicle Maintenance & Repair! I'm not an AC expert (by any shake), but wondering if the compressor is dying due to a lack of PAG oil. Also, did you vacuum out your system prior to refilling with R134a? Jul 27, 2023 at 9:53
  • I did not, in retrospect I'm seeing how I should've approached this. I understand I could have a contaminated system now. Jul 27, 2023 at 19:30
  • Messing up on charge and oil and not vacuuming, those are all major mistakes. Reconsider your qualifications to do A/C work, being careful to avoid Dunning-Kruger self-assessment errors, and either farm out that work, or skill up + gear up. At the very least, a vacuum pump and gage set, so you can do the piping repair and validate that it is is leak-free before taking it to get recharged. Jul 28, 2023 at 19:57

1 Answer 1


This may be as simple as an undercharged system. When converting r12 to r134a, POE oil is added to allow r12 oil become compatible with r134a. This was the quick, down and dirty way to retrofit r12 systems to r134a but no one discusses how much r134a is needed and you cannot use the r12 sight glass as a way to determine r134a amount. With an old compressor, it's probably noisy from less than ideal amounts of refrigerant and old oil. R12 uses mineral oil and not compatible with r134a, hence adding POE oil. Ideally, an old r12 system is flushed of all old oil, the receiver/drier is replaced, new pag oil is added with dye, all O-rings replaced with r134a seals, a complete evacuation using gauges is made to determine if a leak remains or a vacuum holds after shutting off the vacuum pump. If a vacuum holds after 15 minutes, this means the repaired/rebuilt system can hold pressure. If a vacuum leaks atmospheric air back into a system, there's a leak that will not hold refrigerant. Ac repairs are not diy friendly and require refrigeration knowledge. A repaired system holding a vacuum should hold refrigerant. Adding r134 (at least one can with dye or a small vial of dye added when the system was open) is injected into the low/suction side before starting the engine. Both gauges are monitored when injecting refrigerant. One key is to add the second can a few ounces at a time then allow system pressures to stabilize. Stop adding r134a when low side pressures remains around 29-35 psi. You may have to run a high idle, around 1200 rpm, for optimum system pressures. No one drives at idle speed and operating pressures varies in proportion to engine rpm. It's easy to over fill a system with high side pressures exceeding 250 psi. Compressors have a safety relief valve to open of pressures exceed 450 psi. Low side pressure is the key to determining lowest temperature and pressure, always above freezing (32°F).

Ignore static pressures; once a hot ac system stops, high pressures continues to be released thru the thermal expansion valve that remains open. Both gauges are showing high pressures releasing thru the txv with low side pressure jumping up as soon as ac is turned off, whether from the combination low/high pressure sensor or manually shutting off ac. While the txv varies release of high pressure liquid to maintain low side pressures that correlates to above 32F (preventing creation of an ice box from moisture condensing on the evaporator coils), additional info leads me to ask you a cooling fan question. Does this system have an electric cooling fan in front of the condenser coil or behind the radiator (or both) and is/does it/do they run when ac is turned on? The best troubleshooting feedback was mentioning water spray on the condenser coils, immediately dropping high side pressures from 300 down to 160 psi; lack of cooling fan operation. Either you have an older clutch fan that's worn out and not engaging to pull in airflow thru condenser and radiator, missing/damaged cooling fan shroud or the electric fan(s) are dead/running at the wrong speed (some vehicles have two fans with three electronically controlled speeds). Ac must have fan(s) running since the compressor creates high pressures and heat at the discharge side, feeding hot refrigerant into the condenser coil in front of a hot radiator. Condenser coil and radiator must have fan cooling when ac is running otherwise overheating/higher than normal ac pressures occur and the radiator may overheat. Fan cooling seems to be the problem and you haven't mentioned amount of original refrigerant (r12) or replacement r134a, which adds to this errant ac system not operating ideally.

  • Lots of knowledge here ... thank you for the education. +1 I'm actually thinking about converting a 91 Z28 I have over to R134a. Your information here should help a lot. Jul 27, 2023 at 16:30
  • @Paulster2, whether a diyer or pro, I consider vehicle ac systems as complicated as either turbo or superchargers. Each has its own complexities and not diy friendly. Thorough knowledge is the key to diagnosing, troubleshooting, and repairing ac systems. The same for turbo/supercharger systems.
    – F Dryer
    Jul 27, 2023 at 16:38
  • While I stated I'm not an AC expert, I've ridden in the rodeo before. I done a lot of successful work on AC systems in the past. Nonetheless, I appreciate your experience and knowledge on the subject. Jul 27, 2023 at 16:58
  • I don't know if this helps but my low side pressure is around 50 psi. I live in the south and it was around 80 degrees when I checked in the morning. Temps can easily get to 95 where I am. Jul 27, 2023 at 19:33
  • @LucasDeane - Is that 80 psi with the AC running or not running? If not running, the system would be equalized, which means that's not a lot of pressure. Jul 27, 2023 at 19:54

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