Are These A/C System Pressures Reasonable?
#1
06-09-2024, 12:51 PM
Are These A/C System Pressures Reasonable?
Car: 2004 Accord LX, 4 cyl, 5-speed auto
Last summer my A/C started blowing warm air when the outside air temp would get above around 85°F, and I was doing city driving. I got the A/C leak-checked in October 2023 (no leaks immediately found, schrader valves replaced), but the problem remains. I haven't been able to duplicate the problem behavior in the garage, which is the compressor cycling on/off every 2-3 seconds. However, I did put together a video:
of running it in the garage with a pressure manifold hooked up to the system. Maybe one of you experienced A/C guys can tell me if these pressures look right, or if my system is badly over- or under-charged. Note that in the video I'm not turning the A/C compressor on and off, the ECM is commanding that (it is manual A/C set to max cool). Another note: I get no trouble codes for the HVAC. Thanks for taking a look!
Last summer my A/C started blowing warm air when the outside air temp would get above around 85°F, and I was doing city driving. I got the A/C leak-checked in October 2023 (no leaks immediately found, schrader valves replaced), but the problem remains. I haven't been able to duplicate the problem behavior in the garage, which is the compressor cycling on/off every 2-3 seconds. However, I did put together a video:
Last edited by MtnFlyer; 06-09-2024 at 12:57 PM.
#2
06-10-2024, 11:08 PM
I moved your post to the proper forum to get answers.
What work have you done on the system so far? Have you added R-134A and how much?
The Honda procedure has the a/c set to max cool, recircuilate, all doors and hood open, and at 1500 rpm. Glove box also have the dampeners removed and the glove box is hanging down (like when you change the cabin air filter). The "ambient" air temp is the temperature of the air near the glove box. They also want you to measure the temperature from the outside vents. The procedure says no passengers in the car, so you can reach with your hand to raise the rpm.
If using 80 °F, the low side should be around 18 psi, and the high should be around 175 psi @1500 rpm.
Just from your video, your high side pressure is high.
What work have you done on the system so far? Have you added R-134A and how much?
The Honda procedure has the a/c set to max cool, recircuilate, all doors and hood open, and at 1500 rpm. Glove box also have the dampeners removed and the glove box is hanging down (like when you change the cabin air filter). The "ambient" air temp is the temperature of the air near the glove box. They also want you to measure the temperature from the outside vents. The procedure says no passengers in the car, so you can reach with your hand to raise the rpm.
If using 80 °F, the low side should be around 18 psi, and the high should be around 175 psi @1500 rpm.
Just from your video, your high side pressure is high.
#3
06-11-2024, 02:02 PM
PAhonda, thanks for moving my post to the right forum. And thanks for the info on the pressures/methods. Here's what I've done so far:
- cleaned condenser (compressed air and water, exterior)
- swapped around the A/C relays to see if there was a bad one. There wasn't.
- when serviced at the shop in October, I was charged for 2 "units" of R134A at $24.99 ea, but I don't know how much they put in my system.
Today it's working great (blowing cold), but outside air temp is about 80°F. I have a suspicion that because it may be overcharged, I'm tripping the high-pressure cut-off when it gets really hot out and I'm in stop-and-go traffic (the manual indicates the high pressure cut-off occurs between 370-455 psi, and I'm seeing pressures in that range). I don't have a way to remove refrigerant, so a trip to the shop may be in order.
- cleaned condenser (compressed air and water, exterior)
- swapped around the A/C relays to see if there was a bad one. There wasn't.
- when serviced at the shop in October, I was charged for 2 "units" of R134A at $24.99 ea, but I don't know how much they put in my system.
Today it's working great (blowing cold), but outside air temp is about 80°F. I have a suspicion that because it may be overcharged, I'm tripping the high-pressure cut-off when it gets really hot out and I'm in stop-and-go traffic (the manual indicates the high pressure cut-off occurs between 370-455 psi, and I'm seeing pressures in that range). I don't have a way to remove refrigerant, so a trip to the shop may be in order.
#4
06-11-2024, 08:28 PM
I'd probably ask the shop to evacuate the system, check that the system holds vacuum (so no leaks), then recharge with the OEM weight of R134a. There should be a sticker under your hood with the recommended amount. The shop manual says 17.6-19.4 oz (500-550g).
The a/c pressure switch on the high pressure line will cut off at <28 psi and >455 psi, so your a/c is cycling for some other reason at idle.
If you have the correct amt of R134a in the system and still get high pressures, then you likely have a blockage in the high pressure side of the system. If you get to the point of replacing parts, then I'd recommend replacing every o-ring in the system and probalby the expansion valve and dessicant. Once you get the system sealed, they tend to work trouble-free for a long time.
The a/c pressure switch on the high pressure line will cut off at <28 psi and >455 psi, so your a/c is cycling for some other reason at idle.
If you have the correct amt of R134a in the system and still get high pressures, then you likely have a blockage in the high pressure side of the system. If you get to the point of replacing parts, then I'd recommend replacing every o-ring in the system and probalby the expansion valve and dessicant. Once you get the system sealed, they tend to work trouble-free for a long time.
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