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Matt Mallard
Matt Mallard, ASE Certified Technician
Category: Car
Satisfied Customers: 8
Experience:  15 years auto mechanical repair, 8 years auto insurance estimating, repair shop negotiations
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97 Hyundai Accent: only 235,000 miles..compressor..vacuum..20 minutes

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Hi, Guys, I've got a 97 Hyundai Accent with only 235,000 miles on it and the A/C compressor died. I replaced it and also the drier and after putting the vacuum on it for 45 minutes I charged it up.    It works great for about 20 minutes and then blows warm air.   If I turn it off (engine) for a couple minutes it will blow cold air again for a while. I don't believe it is air as I followed the instructions very carefully. Any ideas?
Welcome to JA!

What is the outside (ambient) temperature?
I'll assume that there are two cooling fans on the back of the radiator? Are they both running and drawing heat?
Customer: replied 8 years ago.
This is Florida. It is 90 out there. There are 2 fans on the car and they both are working. Are they drawing heat? Don't know. Good question. I could test it but it would take 20 minutes before I could answer that
Sufficient air flow through the condenser is one place to start.
Also, it is possible that the compressor clutch may be weak.

Do you have a way to check for voltage and ground to and from the pressure sensors and to the compressor clutch? That info will be helpful along with the low and high pressure readings before the compressor kicks out.

Customer: replied 8 years ago.

The compressor and clutch are both new and while it it blowing warm air it never disengages or didn't while I was observing it for a few minutes.


The pressure on the low side was around 35 and on the high side was about 240. Of course that was when it was cooling. Didn't check it when it stopped.


Your point about the fans has me wondering. They both ran when I charged it but I don't know if it was running 20 minutes later. That fan has seen a lot of use.


By pressure sensors, do you mean the pressure switch on the drier? I can certainly get that but probably can't get back to you till late tomorrow or Mongay if you don't do weekends.

Customer: replied 8 years ago.

What the heck is going on? Am I supposed to be on your web page or on my Email? Dealing with Matt was fine but they switched me to somebody and then I have several Emails.


Please advise as I'm confused. Of course I'm 77 so maybe that is the reason

Hello TigerBill. Matt here.
I'm not sure about the emails that you are getting and apologize if there is some type of system issue going on. I just answer questions and help folks between dealing with 3 boys.

If we are going on the assumption that there was no problem with the evacuate and recharge, no air in system etc. then the pressures at the time that cooling stops really are important to know.

I would not go out and buy cooling fans or switches until we can establish what exactly is going on in the system. It is important for me to know the pressure readings at the time that the cooling stops and right beforehand.

Does the warm air start after 20 minutes idle or do you when driving the vehicle?

Customer: replied 8 years ago.

It happens when I'm driving. I've never let it idle for that lenght of time so I don't know if it would or wouldn't.



Tiger Bill,

Aside from monitoring pressures you cannot assume that the new compressor and clutch assembly are not acting up.

Let it idle for awhile, while idling and safely secured, give it some RPM and monitor the pressures.

I just actually had a similar issue on one where the compressor clutch was weak. It was fine at idle and would kick out when the RPM increased. Even a new compressor clutch can do this if too many spacers are installed.

I'll continue monitoring and will help you through this.

Customer: replied 8 years ago.

OK, Thanks Matt. It is 9:30 and I have to get up at 5am and go to work. How can we continue this. Will you be around tomorrow afternoon or Sunday or when. I'm off Sunday and work 2:30 to 10 normally during the week.


Incidently, I can see the compressor pretty good and if it is slipping, it sure has me fooled.


But then again, I find things are not always as they seem.


I'll have those pressures for you next time we chat


I'll wait for your reply before I shut down. Cheers

Tiger Bill,
That will be great. I'll be off and on all weekend.
Customer: replied 8 years ago.
So how do I ask for you?
I'll be monitoring the posts every couple of hours during the weekend. If another person pops up with your solution in the mean time, that is really what matters most.
I've volunteered for these types of sites for years and do it because I love to help people.
I also understand that no technician has every answer at a given point in time so if someone is able to help you right away and get this fee, that is cool with me.
What matters is that we are collectively able to help you out here.
Customer: replied 8 years ago.

Good morning Matt,


I put in 11 hours yesterday so I didn't get on the web.


Here are the stats.


Overnight the pressure for both sides is 75.


When I start it and it is blowing cold air the pressure is 150 high and 20 low. When it cycles off it drops to 125 high and 50 low.


When it no longer blows cold air the pressure is 125 high and vacuum 10 on the low.


Does that help?



Howdy Bill,

I'm not sure if this was the problem to start with or if it has leaked since Friday, but it is low on refrigerant.

Where you started out at with low around mid 30's and high in mid 200's is where it should be.
Customer: replied 8 years ago.

Hi, Matt,


I added a half can of freon last night and the most I could get on the high side was about 170. I said it was 240 on an earlier post but I'm thinking I posted what I read it should be. not what it really was. (I didn't write it down and even when I do I sometimes doubt my figures.)


Anyhow, the pressure was over 100 this morning on both sides and that is TOO high. There are no leaks as it will hold vacuum for 3 hours.


What I did find, though, while searching the web was a defective expansion valve will cause low pressure on the high side and can cause even a vacuum on the low pressure side. With the extra freon in I had a reading of MINUS 10 on the low side.


So at this point what I want you to do is verify whether this is true as I seem to fit the criteria.


I'm not in any hurry for an answer as I can't do anything till this weekeend but if a expansion valve sounds resonable, I'll hit the accept and send you on your way.


I think I'd rather replace the timing belt or have a root canal than remove the dash to get that thing out of the evaporator. No, forget the root canal.


Thanks for your help Bill

Hello Bill,

Yes, a bad expansion valve can cause both low pressure on the high side and a vacuum reading on the low side.

You mentioned that this am the readings were over 100 on both sides but didn't say if that was with the compressor off or on. If the compressor is off, then that would be about normal.

It does not appear that this vehicle has an orifice tube which is generally the case if there is an expansion valve. If the old compressor had an internal failure, it very well could have sent debris into the expansion valve. Given the miles on the vehicle, it really should be changed.

I cannot get into my database for a few hours but will be getting some detailed info on how to change it.
I'm pretty sure that the whole dash will NOT have to come out,, just the glove box area and inside box.
Customer: replied 8 years ago.

Great, Matt. I'll hold the hitting the accept button till I hear from you. The manual says the dash has to be removed BUT it covers 86 thru 98 and I never know when or if they are referring to my car


Cheers Bill

I have found the info.

Disconnect battery.
Discharge a/c system
Disconnect the high and low lines from under hood at firewall.
Cover the open fittings to keep contamination out of system.
Remove evaporator drain hose.
Remove grommet cover from dash panel (two screws).
Remove glove box assembly (3 bolts)
Evap box is right there,,   disconnect electrical connector(s)
Remove 3 evaporator box bolts (nuts)
Remove box.
Remove box bolts and split box
Evaporator and expansion valve are inside of box.

Not too bad really.

Matt Mallard and 12 other Car Specialists are ready to help you
Customer: replied 8 years ago.

Matt, thank you so much. It was certainly worth the price of admission. Maybe we can work together again some day. Money well spent


Cheers Bill

Hi Bill,
<br />I'm closing out this question for now but it has been a pleasure working with you and I hope that you are able to get that AC blowing ice cold very soon!