dirtymac Posted August 18 Author Share Posted August 18 Where is this pressure valve located? Got a picture of it ? I wasn't aware of a pressure relief valve in the bullnose AC system... It's built into the discharge side of the compressor manifold. The picture in my original post on this thread has it. I can get you one of it on the truck. The weird thing is that it just drips. I haven't found a lot online about these but the few videos I found show them blowing air, not dripping. Link to comment Share on other sites More sharing options...
viven44 Posted August 19 Share Posted August 19 It's built into the discharge side of the compressor manifold. The picture in my original post on this thread has it. I can get you one of it on the truck. The weird thing is that it just drips. I haven't found a lot online about these but the few videos I found show them blowing air, not dripping. I found it!! Didn’t know that was a pressure relief valve. I always wondered why this system was allowed to function without any high side pressure switch… I am seeing some old ooze but nothing significant. Link to comment Share on other sites More sharing options...
viven44 Posted August 19 Share Posted August 19 When we got started this morning the ambient temperature outside was around 88. The static pressures from the Low and High side were just above 100psi. From the charts I have found this appears to be accurate. We ran everything for about 20 minutes. No leaks. Low pressure hung around 50psi and High pressure around 330psi. Using 90 degrees for the ambient temperature, the Low pressure was good and the High pressure was High. After cutting the A/C off it equalized to about 105psi. After that we let everything sit for about an hour. By this point the outside temperature was 95. The static pressure was still about 110psi. Everything ran for about 10 minutes and then the pressure relief valve started to drip (slower than last night). Low side pressure was 55psi and High side pressure was 350psi. Now came the fun part. We turned off the A/C and let the static pressure equalize. The plan was to unplug the gauges, reset evertyhing, and test again from scratch. I'm not sure what happened in the frenzy that ensued but when we removed the Low side connector the schrader valve stuck open. It took us several minutes to get the thing straightened back out and stop the leak. We definitely lost some Freon. Started everything back up. Pressure valve is still leaking at this point. Low side pressure has now dropped to about 40 psi and High side has dropped to 295psi. This would seem consistent with the loss of Freon but the pressure valve is still dripping until we turn the A/C off. We are wondering about all of the talk of Ambient temperatures. Sure, it's 96 outside at this point, but under the hood its probably 110 or higher. Is that affect the pressure release valve? Could it just be bad? I haven't been able to locate any specifics on the valve other than what it does. Your pressures were definitely high and I’m glad you had that leak It’s very strange that pressure relief valve is still leaking though. May be time to replace it. I think the one you found on Rockauto seems to be the correct one https://www.rockauto.com/en/moreinfo.php?pk=3102783&cc=0&pt=6696&jsn=318 PS: I just read above and noticed the comments from others identifying it as the pressure relief valve Link to comment Share on other sites More sharing options...
mat in tn Posted August 19 Share Posted August 19 Your pressures were definitely high and I’m glad you had that leak It’s very strange that pressure relief valve is still leaking though. May be time to replace it. I think the one you found on Rockauto seems to be the correct one https://www.rockauto.com/en/moreinfo.php?pk=3102783&cc=0&pt=6696&jsn=318 PS: I just read above and noticed the comments from others identifying it as the pressure relief valve there is another point to bring up. all of these temp pressure variances are also dependent on available air flow. the pressures will be higher if the thermostatic fan clutch is failing to engage enough. are you able to hear the fan engage and "load up" as temps rise? on a properly operating one you can often hear the air flow cycle in a range of stronger, weaker, stronger, weaker continuously at operating temp with ac on the rate will vary up to the point of continuous at higher temps. and yes it will be different with the hood closed and or driving. Link to comment Share on other sites More sharing options...
85lebaront2 Posted August 19 Share Posted August 19 I found it!! Didn’t know that was a pressure relief valve. I always wondered why this system was allowed to function without any high side pressure switch… I am seeing some old ooze but nothing significant. These systems pre-date the high pressure switch. The relief valve is the safety on them. High pressure switches came into use when the government regulations required full containment for refrigerant. One of the steps in doing an R134a retrofit was to remove the relief valve and replace it with a high pressure switch. I only had one vehicle that I couldn't convert, a 1985 Chrysler Lebaron convertible. The condenser design and mounting did not get adequate air flow when sitting still which resulted in tripping the high pressure switch, or burning up the compressor drive belt. Link to comment Share on other sites More sharing options...
viven44 Posted August 19 Share Posted August 19 These systems pre-date the high pressure switch. The relief valve is the safety on them. High pressure switches came into use when the government regulations required full containment for refrigerant. One of the steps in doing an R134a retrofit was to remove the relief valve and replace it with a high pressure switch. I only had one vehicle that I couldn't convert, a 1985 Chrysler Lebaron convertible. The condenser design and mounting did not get adequate air flow when sitting still which resulted in tripping the high pressure switch, or burning up the compressor drive belt. Thanks.. great info Bill, I need to source a high side pressure switch for future use... Link to comment Share on other sites More sharing options...
dirtymac Posted August 20 Author Share Posted August 20 there is another point to bring up. all of these temp pressure variances are also dependent on available air flow. the pressures will be higher if the thermostatic fan clutch is failing to engage enough. are you able to hear the fan engage and "load up" as temps rise? on a properly operating one you can often hear the air flow cycle in a range of stronger, weaker, stronger, weaker continuously at operating temp with ac on the rate will vary up to the point of continuous at higher temps. and yes it will be different with the hood closed and or driving. In fact, we have been discussing this as a possible issue for the last several weeks. We have been dealing with some high coolant temps the last few weeks. I suspected most of the problem was our radiator, which has developed a small hole above the intake hose. It doesn't leak (that we have seen) but it does steam. Water usage has been minimal. While working on the A/C, we discovered that even full, with good water flow, the engine coolant was still getting hotter than normal while parked. We ordered a new radiator last night. We had been putting this off until after the A/C was done because we have a heater core bypass valve to install, and a new thermostat. This morning we were discussing the fan clutch again and decided to go ahead and replace it. We are not hearing the click some people mention or the fan loading up. It generally seems to turn the same, winter, summer, fall, etc. We have a severe duty clutch on order. If all goes to plan, we will have all of that and the pressure relief valve installed this weekend. Link to comment Share on other sites More sharing options...
dirtymac Posted August 20 Author Share Posted August 20 These systems pre-date the high pressure switch. The relief valve is the safety on them. High pressure switches came into use when the government regulations required full containment for refrigerant. One of the steps in doing an R134a retrofit was to remove the relief valve and replace it with a high pressure switch. I only had one vehicle that I couldn't convert, a 1985 Chrysler Lebaron convertible. The condenser design and mounting did not get adequate air flow when sitting still which resulted in tripping the high pressure switch, or burning up the compressor drive belt. Do you know of a high pressure relief valve for the factory manifolds? Link to comment Share on other sites More sharing options...
mat in tn Posted August 20 Share Posted August 20 Do you know of a high pressure relief valve for the factory manifolds? if you are thinking of an extra high pressure then no. I would not do that anyway. that would be a similar thing to putting a 30 amp fuse in a 10 amp circuit. I have not heard any "click" before from a fan clutch but have always listened for the load change from the air flow. get as good of a radiator as you can. I use factory replacements mostly but will go as large of capacity as is available. many go with fabricated aluminum, and I like them too, but I still prefer the factory look for most of my vehicles. Link to comment Share on other sites More sharing options...
viven44 Posted August 20 Share Posted August 20 if you are thinking of an extra high pressure then no. I would not do that anyway. that would be a similar thing to putting a 30 amp fuse in a 10 amp circuit. I have not heard any "click" before from a fan clutch but have always listened for the load change from the air flow. get as good of a radiator as you can. I use factory replacements mostly but will go as large of capacity as is available. many go with fabricated aluminum, and I like them too, but I still prefer the factory look for most of my vehicles. What does the 'click' mean ? For anything I have recharged myself, I usually go by the chart on the factory manual (ambient temp, low side, high side).... the ambient temp chart is important because when the recharge is done the hood is open so the ambient is the dominant factor..... I have come across trucks that had a 'click'... so I was wondering what that meant.. Link to comment Share on other sites More sharing options...
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