My first thread. On Friday I bought a 96 850 GLT, my FIRST Volvo! I will have to replace the odometer gears, yay.... Also, I would like to know if anyone has an idea why my AC blows cool, but not cold air in the sun/hot weather? It blows cold at night. The previous owner said he couldnt figure it out. He took it to an AC shop and they couldnt figure out what it was. The refrigerant is not leaking and properly filled. Any ideas?

 

That was the symptom on my VW. The compressor ended up dying a year later. My guess is the lower temp at night is a direct result to the lower temp of the ambient air, but that's just a guess.

 

I have a similiar problem - when driving down the freeway its ok, but then when I exit the freeway and sit at a few lights, the AC blows warm, Also if I floor it the AC shuts off like its supposed to, but it never comes back on.

According to Tech and a few others my compressor needs re-shimed, when things heat up the compressor clutch slips or cant hold. Sounds like a good job for me to work on this fall when I dont need AC. Yours may have the same problem, but more often then mine.

 

There are quite a few threads regarding the issue. Try in-forum search.

The A/C is known to fail on the 850s for the following reasons:

- Compressor needing re-shimming: https://volvoforums.com/m_34431/tm.htm
- The evaporatour needing replacement: https://volvoforums.com/m_7364/tm.htm
- Pressure/temp switch on the compressor shutting down the compressor at high temp.

The last one requires jumping of the wires on the compressor or the low pressure switch near the firewall. I would first try an aftermarket recharge kit to check for the systems pressure. The correct pressure should be 25-33 PSI on theLOW side.


JPN

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JPN, thanks for the links. I actually bought that recharge kit when i had th 97 960. So I just need to find out where the LOW side is located at on the 850. Thanks!

 

It should be on your left as you face the engine from the front. There should be two lines that run under or around the ECU and coolant reservoir. One line should have a tap on it for the low side port. There should be a cap that says something like Max 6 Nm. It's visible in the first, fourth and fifth pictures on this thread: https://volvoforums.com/m_62590/tm.htm. (At least, I think it's similar to the V70 that I'm driving.)

 

On the left of the engine cabin, close to the firewall you have the low pressure switch. Follow that line and you will find the low pressure service port close to the front left headlight, beside the windshield water reservoir

 

found it, thanks! so, does anyone know what else it could be? If the evaporator is bad, the lines on the firewall will be frozen, right? the blower works just fine but i liked the writeup with pix 99v70 did on replacing it. so is it possible to replace the evaporator(if necessary) without taking off the entire dash??? thanks again for the help....

 

No there's not.

 

ok, so I saw Tech's writeup with pix but didnt see a picture of the actual location of the evaporator. I think it is behind the blower motor, right? anyone have pix of it against the firewall?

 

Ok, today was hot during lunch. 90F+ and about 75% humidity here in houston. It was frustrating that the AC didnt cool at all. So when i got back, i did ALOT of searching and reading. I now have basic knowledge of what the major components in the AC system do.

FIRST, the car has not been retrofitted with the cabin air filter. I will order and get it installed soon as possible.

SECOND, I read about replacing the evaporator and after rereading three times, I am confident I can get it done if I have all the tools in one day. It doesn't seem too difficult, just time consuming.

Troubleshooting the AC: When I got home, checked the clutch. It engages and disengages on demand as it should. I didnt see any malfunction in it's performance. Next, I found a R134 hose with integrated gauge that I got last summer from Oreilly auto parts. It read almost 60PSI, which I know is TOO high. I am not sure if the gauge works properly though. So there is no need to recharge it(an easy fix).

So, what do I check next before replacing parts? what can be causing cool/ambient temp air to come out of the vents when the ac is on high w/out the recirc engaged? I worked on the car in underground parking, so the sun wasnt beating down on me. My car has ECC, so I figured there has to be an internal temp sensor. Where is it located and does it cause this problem?

Thanks for the help!

 

I would be concerned about that pressure. Was the pressure changing at all while running? It'll be hard for the compressor to be very efficient with that much pressure ahead of it. I'm not sure what the exit pressure of the compressor is designed for, but if the inlet pressure is double what it's designed for, at the very least it won't be efficient.

 

I didnt notice it change. however, like i said, it is a cheapo gauge that came with a can of r134...any other suggestions?

 

Sorry I just read back over this and thought I'd answer your earlier question. Besides Tech's great write-up, chuck just recently posted this one that has a link to a pdf that would be very useful. Near the end you can see a picture of the plastic housing that the evaporator sits inside of. The picture shows the entire assembly removed from the car and then opened up to expose the evaporator. It doesn't look like it'd be possible to take a picture of it against the firewall since it's fully enclosed in the plastic housing. https://volvoforums.com/m_75143/tm.htm

I'm definitely no expert in diagnosing problems, so this is just my two cents.
I would see about getting an accurate gauge or finding someone who will check the pressure for free. I would check the pressure while it's running with the a/c on. As I recall, if you are low on refrigerant you should see the pressure increase until the compressor kicks on and then it'll drop until the compressor stops running. If you have a good amount of refrigerant, you should have steady pressure. If you really do have steady pressure that is at 60psi, I'd see about getting it recovered (discharged) until the pressure is around the range that JPN noted (25-33psi).

My theories are the following (assuming the compressor and clutch are working properly as you said):
1) You are low on refrigerant - this is what I'd expect if the air feels cool (cooler than ambient air) during the day and cold at night. A little bit of refrigerant will allow some heat transfer to take place and bring the air temperature down by a little bit. If this is the case, then your gauge is totally wrong.
2) You have too much refrigerant - I'm not sure exactly what this would cause, but if your compressor inlet pressure is higher than the designed exit pressure, the laws of physics would say that the pressure should go through the compressor in the wrong direction. In actuality, the compressor operates to push the refrigerant through by a series of openings in the chambers so I'm not sure there is a pathway that would allow the refrigerant to flow backwards. Regardless, this would definitely reduce the efficiency/effectiveness of the system. Basically, if the pressure is that high, when the refrigerant passes through the expansion valve (orifice tube), the temperature will not drop as low as it should. Basically, the pressure and temperature of a fluid are directly related. The way the a/c works is by going through a series of pressure and temperature changes so that the pressure and temperature are both low when it gets to the evaporator. If the pressure is still high at that point, then the temperature would also be high and therefore not provide as much cooling effectiveness.

I'll try to scan in my diagram from my days work at an HVAC/R company where we primarily designed refrigeration systems for grocery stores. Those systems were much more complex, but the principles are the same. Anyway, the diagram (which I don't have in front of me) shows how the temperature and pressure varies throughout the system. I've never found a diagram that was as easy to understand.

Anyway, those are my thoughts. Hope that helps.

 

makes sense, I will see what I can do during lunch about getting it evacuated and recharged. Any other ideas?

 

Just for a reference, I paid $20 to have mine evacuated at a shop after calling around. I had quotes up as high as $120! Anyway, if possible, you should try to get it evacuated down to the proper pressure and no further, that will save you the recharging.

Also, here's that diagram that I like to use. Hopefully it's helpful to someone. It's obviously different (cars only have one compressor and not some of those other components), but the basic principles are the same. I found it useful when I was tearing down and rebuilding my A/C.

 

wow, so an ACC specific diagnostic tool needs to be used to pull codes related to AC function??? I just ran across this illustration which is why I am asking. Today the AC and RECIRC lights flashed. It is the first time this happens even though that AC cooled better than during the day yesterday.


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I've read a post or two about those flashing lights. I think Tech (or maybe JPN) said that Volvo made the system very sensitive so that if any small thing isn't right, those lights will blink. He said that most times it's not actually anything to worry about. Mine blink when I start the car, butsince everything seems to be working well, I just ignore it. (In your case it might be legitimately because the pressure is so high.)

I've never seen anything about retrieving the codes - it's interesting to see there is something.

 

Ok, i got the system running at about 35PSI now. Guess I will wait and see what happens. It still isnt ice cold like I would expect it to work...so I am not sure what to do next if it doesnt get better.

 

If the compressor is running, the clutch is engaging, the pressure is right and the fan is working, I'm not sure what could be wrong. I wonder if there's a way that something would screw up so that coolant is running to the heater core even when the a/c is. Would that cause cool air due to a mixture of the cold and hot/warm air?