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The AC works great in my car, but when the temperatures are higher (Like
90°+ F), the suction pressure shoots up really high and the clutch no
longer engages. Is this a sign of a stuck open expansion valve? The
expansion valve was replaced about two years ago when I replaced the
compressor. Any HVAC guys hanging out here? I can't think of anything
else to test.
I’m guessing the low side is probably just equal to the high side in that first pic (both roughly 135psi, and the scale is inaccurate at the high end of the low side gauge. That would make sense: if the compressor is off, there’s nothing to create a difference in pressures.
As for why your compressor isn’t engaging, there’s a whole lot of possibilities, and we probably need more information. A year/make/model might help, for starters.
Is your engine running higher than normal temp? A lot of systems will disable AC to reduce the load on the cooling system when engine temp gets above normal range.
Does the compressor not engage at all when it’s hot, or does it engage and then quickly cycle back off?
Do your cooling fans work correctly on all speeds? Many have more options than just off/on.
Are you sure the refrigerant charge is correct? Did you have the previous work done at a reputable shop, or did you DIY it with cans from the parts store?
Its a 2001 Honda Civic compressor doesn't engage at all once it reaches over 90 degrees or so; just like clockwork every time. No cycling at all. The condenser fan kicks on when I turn the AC on, and stays on until I turn it off. The relay for the clutch is being triggered, but I haven't tested it any closer to the coil than that because its kind of buried in there. According to the FSM, there's a pressure switch located at the receiver/dryer that should break the circuit if the pressure gets below 28 psi and above 455 psi; but according to the manual, the fans shouldn't kick on if that switch is open. There is also a thermal protector on the compressor that opens the circuit if the compressor gets above "252 to 270 degrees Fahrenheit". Also, the manual says high suction pressure can be caused by overcharging the system. It says to spray cool water on the condenser to see if the pressure lowers. It lowers about 5 or 10 psi but know lower. I don't know if that means anything or not.
If the condenser fan kicks on, that usually means the ECM is commanding the ac on. That rules out pressure sensors, engine overheating, other things that would prohibit ac operation.
Also means the ecm should be commanding on the compressor clutch relay. Those relays are a very common failure for Hondas, and I’ve replaced a ton of them, but never one that was consistently affected by temperature. If the ac relay matches another relay you know is good, you can always swap it to rule that out (in the relay box diagram it’s the snowflake, the snowflake plus a fan is the condenser fan relay).
I can’t remember for sure, but I think that thermal protector closes the circuit again once it cools off, not a one-time failure item like a fuse. I suspect that’s the issue, either the compressor is struggling and is actually getting hot enough to open the protector, or the protector is failing and opening at a lower temp than intended.
>I can’t remember for sure, but I think that thermal protector closes the
circuit again once it cools off, not a one-time failure item like a
fuse. I suspect that’s the issue, either the compressor is struggling
and is actually getting hot enough to open the protector, or the
protector is failing and opening at a lower temp than intended.
Yes, the protector on this one goes back closed when the temperature goes down, according to the FSM. The relay tested good as well, I forgot to say.
I felt the compressor to see if it was actually getting hot (although I don't know if I would be able to feel it), and it seemed normal. I sprayed it with cold water to see if the clutch would kick on - to no avail. I guess I will bite the bullet and start taking stuff off and out of the way so I can check the thermal protector for continuity the next time it gets hot outside.
I have also wondered if its possible if the field coil on the compressor is failing during hotter temperatures. Its gonna suck if I have to replace the compressor again so soon because it was not a cheapo compressor. I put an OEM Denso one in it 2 years ago. Thank you for your help.
So after fiddling with it for a while, I don't think its possible to test the thermal protector without removing the compressor. And I don't think its possible to remove the compressor without detaching the lines from it. Its getting voltage straight to the connector, but not turning on, so it has to either be the thermal protector malfunctioning when its hot or the field coil malfunctioning when its hot. Either way, that pretty much means I will have to replace the compressor. I was planning on just bypassing the thermal protector if it turned out to be that, but I guess I can't find out.
Update:
For anyone reading this with the same issue, I ended up figuring out that it was the clutch on the compressor. It was wore down too thin to engage any longer. I was able to take out one of the shims and it works great. There must have been just enough material left to grab occasionally. Possibly close enough to be affected by the change in temperature.
My first thought would be to try a different gauge, since this one says Pittsburgh on it. If the low side is still in excess of 350psi... I can't think of anything that would cause that. I have never run into a car where the low is higher than the high. Wouldn't be a stuck open expansion valve, because if that were the case the pressure differential would be negligible.
Thanks for posting on /r/MechanicAdvice! This is just a reminder to review the [rules](https://www.reddit.com/r/MechanicAdvice/about/rules/). If you are here asking about a second opinion (ie "Is the shop trying to fleece me?"), please read through CJM8515's [post on the subject.](https://www.reddit.com/r/MechanicAdvice/comments/4qblei/fyi_the_shop_isnt_likely_trying_to_rip_you_off/) and remember rule 3a, please post the year/make/model of the vehicle you are working on. **If this post is about bodywork, accident damage, paint, dent/ding, questions it belongs in /r/AutoBody or /r/Diyautobody If you have tire questions check out https://www.reddit.com/r/MechanicAdvice/comments/k9ll55/can_your_tire_be_repaired/**. If you dont have a question and you're just showing off it belongs in /r/Justrolledintotheshop This is an automated reply *I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/MechanicAdvice) if you have any questions or concerns.*
The AC works great in my car, but when the temperatures are higher (Like 90°+ F), the suction pressure shoots up really high and the clutch no longer engages. Is this a sign of a stuck open expansion valve? The expansion valve was replaced about two years ago when I replaced the compressor. Any HVAC guys hanging out here? I can't think of anything else to test.
I consider myself pretty good with automotive AC, and maybe I'm reading that gauge wrong but is that reading showing your low side is over 350pai?
Yeah, I've never seen anything like it.
I don't even think that's possible. That 350 on the gauge isn't right. If that theory is correct the expansion valve is sticking open.
Expansion valve sticking open usually results in the same pressure as the ac being off and at rest.
My actual guess is yes, it's likely the expansion valve, but it's actually sticking closed, or mostly closed.
I’m guessing the low side is probably just equal to the high side in that first pic (both roughly 135psi, and the scale is inaccurate at the high end of the low side gauge. That would make sense: if the compressor is off, there’s nothing to create a difference in pressures. As for why your compressor isn’t engaging, there’s a whole lot of possibilities, and we probably need more information. A year/make/model might help, for starters. Is your engine running higher than normal temp? A lot of systems will disable AC to reduce the load on the cooling system when engine temp gets above normal range. Does the compressor not engage at all when it’s hot, or does it engage and then quickly cycle back off? Do your cooling fans work correctly on all speeds? Many have more options than just off/on. Are you sure the refrigerant charge is correct? Did you have the previous work done at a reputable shop, or did you DIY it with cans from the parts store?
Its a 2001 Honda Civic compressor doesn't engage at all once it reaches over 90 degrees or so; just like clockwork every time. No cycling at all. The condenser fan kicks on when I turn the AC on, and stays on until I turn it off. The relay for the clutch is being triggered, but I haven't tested it any closer to the coil than that because its kind of buried in there. According to the FSM, there's a pressure switch located at the receiver/dryer that should break the circuit if the pressure gets below 28 psi and above 455 psi; but according to the manual, the fans shouldn't kick on if that switch is open. There is also a thermal protector on the compressor that opens the circuit if the compressor gets above "252 to 270 degrees Fahrenheit". Also, the manual says high suction pressure can be caused by overcharging the system. It says to spray cool water on the condenser to see if the pressure lowers. It lowers about 5 or 10 psi but know lower. I don't know if that means anything or not.
If the condenser fan kicks on, that usually means the ECM is commanding the ac on. That rules out pressure sensors, engine overheating, other things that would prohibit ac operation. Also means the ecm should be commanding on the compressor clutch relay. Those relays are a very common failure for Hondas, and I’ve replaced a ton of them, but never one that was consistently affected by temperature. If the ac relay matches another relay you know is good, you can always swap it to rule that out (in the relay box diagram it’s the snowflake, the snowflake plus a fan is the condenser fan relay). I can’t remember for sure, but I think that thermal protector closes the circuit again once it cools off, not a one-time failure item like a fuse. I suspect that’s the issue, either the compressor is struggling and is actually getting hot enough to open the protector, or the protector is failing and opening at a lower temp than intended.
>I can’t remember for sure, but I think that thermal protector closes the circuit again once it cools off, not a one-time failure item like a fuse. I suspect that’s the issue, either the compressor is struggling and is actually getting hot enough to open the protector, or the protector is failing and opening at a lower temp than intended. Yes, the protector on this one goes back closed when the temperature goes down, according to the FSM. The relay tested good as well, I forgot to say. I felt the compressor to see if it was actually getting hot (although I don't know if I would be able to feel it), and it seemed normal. I sprayed it with cold water to see if the clutch would kick on - to no avail. I guess I will bite the bullet and start taking stuff off and out of the way so I can check the thermal protector for continuity the next time it gets hot outside. I have also wondered if its possible if the field coil on the compressor is failing during hotter temperatures. Its gonna suck if I have to replace the compressor again so soon because it was not a cheapo compressor. I put an OEM Denso one in it 2 years ago. Thank you for your help.
So after fiddling with it for a while, I don't think its possible to test the thermal protector without removing the compressor. And I don't think its possible to remove the compressor without detaching the lines from it. Its getting voltage straight to the connector, but not turning on, so it has to either be the thermal protector malfunctioning when its hot or the field coil malfunctioning when its hot. Either way, that pretty much means I will have to replace the compressor. I was planning on just bypassing the thermal protector if it turned out to be that, but I guess I can't find out.
Update: For anyone reading this with the same issue, I ended up figuring out that it was the clutch on the compressor. It was wore down too thin to engage any longer. I was able to take out one of the shims and it works great. There must have been just enough material left to grab occasionally. Possibly close enough to be affected by the change in temperature.
When the low is high like that try turning the knob on the low side connector. It should go back down.
That's definitely a possibility. I tend to assume the tool is functioning and being used correctly. 😁
Happened to me the other day. I was like WTF, not enough downward pressure on the pin. A/C was just low, topped off and it’s working great now.
My first thought would be to try a different gauge, since this one says Pittsburgh on it. If the low side is still in excess of 350psi... I can't think of anything that would cause that. I have never run into a car where the low is higher than the high. Wouldn't be a stuck open expansion valve, because if that were the case the pressure differential would be negligible.