Automotive Air Conditioning Information Forum

Please give vent temp when providing lo and hi psi. Lo and hi at idle mean little, more interested in readings at 1500-1800. Comp does very little work at idle.

tbirdtbird wrote: ↑Fri Jul 15, 2022 1:20 pm Please give vent temp when providing lo and hi psi. Lo and hi at idle mean little, more interested in readings at 1500-1800. Comp does very little work at idle.

I provided vent temps in the original post and they were unchanged today. The low pressure line coming off of the accumulator would sometimes be very cold and other times not cold at all. The vent temps at the higher rpms would sometimes go lower than idle vent temps and sometimes they would go higher.

70monte wrote: ↑Fri Jul 15, 2022 1:55 pm The low pressure line coming off of the accumulator would sometimes be very cold and other times not cold at all.

Yep, undercharged. My guess is you are right around an empty accumulator. 8oz low.

Best thing to do is have a pro recharge entire charge by weight.

DetroitAC wrote: ↑Fri Jul 15, 2022 2:18 pm

70monte wrote: ↑Fri Jul 15, 2022 1:55 pm The low pressure line coming off of the accumulator would sometimes be very cold and other times not cold at all.

Yep, undercharged. My guess is you are right around an empty accumulator. 8oz low.

Best thing to do is have a pro recharge entire charge by weight.

Thanks. I bet that you are right. That is also what the shop owner told her dad this morning based on what he told the owner about it cycling on and off pretty rapidly at the higher rpms. He is going to give the shop owner the pressures that we got today, and he will go from there.

I had told her dad today after we had gotten the pressure results that we have no idea how much refrigerant is in the system and that it needs to be recovered and recharged to factory specs. We looked for a capacity sticker and there is not one anywhere that we can find. Someone earlier in the thread had said it holds 45 ounces, but I don't know for sure.

70monte wrote: ↑Fri Jul 15, 2022 2:46 pm We looked for a capacity sticker and there is not one anywhere that we can find. Someone earlier in the thread had said it holds 45 ounces, but I don't know for sure.

Right—that was me. The specs that I have for the 2006 and 2007 versions of this truck list 45 ounces of R-134a and 9 ounces of PAG-46, and I wondered whether the shop might have undercharged it.

JohnHere wrote: ↑Sat Jul 16, 2022 9:42 am

70monte wrote: ↑Fri Jul 15, 2022 2:46 pm We looked for a capacity sticker and there is not one anywhere that we can find. Someone earlier in the thread had said it holds 45 ounces, but I don't know for sure.

Right—that was me. The specs that I have for the 2006 and 2007 versions of this truck list 45 ounces of R-134a and 9 ounces of PAG-46, and I wondered whether the shop might have undercharged it.

Well, the AC charge was evacuated, and I vacuumed the system down for 30 minutes and then let it sit for 30 minutes. The pressure decayed slightly so I vacuumed again for about 20 minutes and let it sit for about another 20 minutes and the pressure held. I recharged it with 45 ounces.

Today was slightly hotter at 96 degrees and high humidity. Initially after the charging was complete, low side pressure was 56 and high side was 260. I then had him bring the engine to about 1500 rpms and the low side was around 40 and the high side about 300. I then had him bring it to 2,000 rpms where last time it started cycling the clutch and initially this time it didn't do it and low side was at 32 and high side 350. I had him do this again a little later and the low side would drop to about 22 and the high side about 250 and then the cycling switch would kick the clutch off.

Right before we quit, the idle pressures were at 44 on low side and around 200 on the high side which was pretty much what they were yesterday. The lines coming out of the accumulator were cold and so was the line that was going into the heater box or whatever it is called that attaches to the firewall and houses the blower motor. I did notice that there was cold air coming out around that line which did have some foam around it but was missing some at the top. I don't think air should be coming out of there but I don't know. The other side of that line was hot after the connector, and I believe the orifice tube is located in that portion of the line.

Vent temps at 1500-1800 rpms got down to 57 degrees and at idle were around 60-62 degrees out of the center vent with AC on max and high blower.

We took the truck for a drive and vent temps stayed around 69-73 so I'm assuming the clutch is cycling on and off pretty rapidly. Not sure why it's cycling so much at higher rpms. Could the cycling switch be going bad?

So basically we are back to square one. Not sure what the next step is.

cold air shouldn't be coming out underhood, fix the foam seals or seal it up somehow. If that's jacked up, makes me think the HVAC module was removed at some point, maybe an aftermarket evaporator in there or a badly assembled HVAC module?

I think I'd try troubleshooting heater core problems, maybe a stuck/failed actuator, is there a spot where you can pinch off heater hose either coming or going to the heater core? Also could check performance with a cold engine, also could check vent temperature with the controls set to full cold, but AC not enabled. Also check that with a warmed up engine the controls set to full hot blasts hot air, then full cold, it should go back to ambient plus a little. Heater blend doors are never perfect, vent temp should be 2 to 5F hotter than your ambient air temperature.

DetroitAC wrote: ↑Sun Jul 17, 2022 6:14 pm cold air shouldn't be coming out underhood, fix the foam seals or seal it up somehow. If that's jacked up, makes me think the HVAC module was removed at some point, maybe an aftermarket evaporator in there or a badly assembled HVAC module?

I think I'd try troubleshooting heater core problems, maybe a stuck/failed actuator, is there a spot where you can pinch off heater hose either coming or going to the heater core? Also could check performance with a cold engine, also could check vent temperature with the controls set to full cold, but AC not enabled. Also check that with a warmed up engine the controls set to full hot blasts hot air, then full cold, it should go back to ambient plus a little. Heater blend doors are never perfect, vent temp should be 2 to 5F hotter than your ambient air temperature.

Thanks for the reply. I'm going out of town today until Friday but I will let him know he needs to seal that box up. I told him that the other day too. I also suggested to him he could have a blend door actuator problem.

I'm not sure what the heater hoses look like on this truck or if they are easily accessible. I will have him try the other things you suggested. Thanks again.

Adding to what has already been said:

70monte wrote: ↑Sat Jul 16, 2022 3:41 pm Well, the AC charge was evacuated, and I vacuumed the system down for 30 minutes and then let it sit for 30 minutes. The pressure decayed slightly so I vacuumed again for about 20 minutes and let it sit for about another 20 minutes and the pressure held. I recharged it with 45 ounces.

The vacuum dropping slightly was a sign that air and moisture were still present in the system. Hopefully, you got them all out with the additional 20-minute evacuation.

70monte wrote: ↑Sat Jul 16, 2022 3:41 pm I had him do this again a little later and the low side would drop to about 22 and the high side about 250 and then the cycling switch would kick the clutch off.

We're not concerned with idle-speed pressures because the compressor isn't doing very much at such a low RPM. But at 1,500 RPM and an ambient of 96°F, that's fairly normal operation, and the pressures look pretty good at this point. Earlier, though, they're fluctuating abnormally. The question is, why?

The cycling switch and/or the PCM are turning off the compressor so that the evaporator doesn't freeze up, blocking airflow.

70monte wrote: ↑Sat Jul 16, 2022 3:41 pm The lines coming out of the accumulator were cold and so was the line that was going into the heater box or whatever it is called that attaches to the firewall and houses the blower motor. I did notice that there was cold air coming out around that line which did have some foam around it but was missing some at the top. I don't think air should be coming out of there but I don't know. The other side of that line was hot after the connector, and I believe the orifice tube is located in that portion of the line.

The lines you mention being cold is good. The line from the condenser up to the OT being hot is also good. However, you shouldn't feel any cold air coming out around the line extending from the blower housing. I would seal-up that opening with a suitable caulking or foam.

70monte wrote: ↑Sat Jul 16, 2022 3:41 pm Vent temps at 1500-1800 rpms got down to 57 degrees and at idle were around 60-62 degrees out of the center vent with AC on max and high blower. We took the truck for a drive and vent temps stayed around 69-73 so I'm assuming the clutch is cycling on and off pretty rapidly. Not sure why it's cycling so much at higher rpms. Could the cycling switch be going bad?

Those vent temperatures are not acceptable for a properly operating system. The compressor on your truck doesn't have a control valve, either. It's possible that the cycling switch is going bad, but it seems to me that it's doing its job as intended.

70monte wrote: ↑Sat Jul 16, 2022 3:41 pm So basically we are back to square one. Not sure what the next step is.

At this point, with a truck that has about 230,000 miles on it, I would recover the charge, pull the OT, and examine it. If the OT screen is full of gunk and even some metal particles, that would indicate the compressor is on its last legs. In such a case, I would replace the compressor with a brand-new unit (not rebuilt), the condenser, OT (specs call for a red one), accumulator, and flush or replace the liquid line between the condenser and the evaporator depending on whether it has a muffler. If it has a muffler (I don't believe it does), you'll need to replace the line because mufflers can't be flushed.

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