1998 V70 - AC- where is evaporator sensor ?

Molibius · Post by **Molibius** » 15 Jul 2013, 16:33

The AC is freezing up. Somone on the forum said it could be due to evaporator temp sensor.
The problem I have - my Volvo does not have the sensor on the left side lower dashboard panel as per pics on the web. So where is it ?
Expansion valve could be a problem to but again, we can't find it.
I just put brand new AC compressor and it was not by the compressor and not in the ac pipes going into firewall .
We talk about V70 -1998, base model.
Any ideas ?
Thanks for reading

Post by **Ozark Lee** » 15 Jul 2013, 16:47

There is no thermostat on the evaporator on a '98. Also, there is no expansion valve but rather an orifice tube to do the same thing.

Usually when there is a freezing up problem it is due to a low R-134A charge. In most cases the low pressure sensor kills the compressor when the pressure gets low enough to freeze but you wouldn't be the first with this problem. If you can get a low side pressure reading while the system is running and post the number back that will pretty much tell us what we need to know to help you out.

...Lee

Post by **jblackburn** » 15 Jul 2013, 16:47

There isn't one.

Evaporator freezing is prevented by the high and low pressure cutout switches. If youre sure that the charge level is correct, then one of the switches isn't cutting out when it should.

Edit: never mind, Lee beat me to it.

Post by **jimmy57** » 15 Jul 2013, 17:06

Faulty pressure switch can do this or a bit of overcharge makes CCOT systems freeze up. The low side pressure must drop to 23-24 for compressor to go off when working properly. If the switch is faulty then this doesn't happen. If the system is overcharged a little then it still works fine but the low side pressure will not drop readily to 24. If it hangs at 25-26 then it freezes after a while. WHen overcharged it may still cycle but not often enough and not off long enough for a thaw of evaporator.

Molibius · Post by **Molibius** » 15 Jul 2013, 17:21

Thanks,
The mechanic did over charged the system.
I think it should be charge at 30 psi and he put 40 because we suspect slow leak from evaporator .
So that could be the problem.
I will keep an eye at the pressure and keep update.
Thanks a lot guys You are the best

Molibius · Post by **Molibius** » 19 Jul 2013, 17:15

This is a bit crazy. The pressure at the charging port reads about 80, the other day was around 50.
The mechanic said that this time he did not overcharged the system.
The AC compressor works, one of the tube going into fire wall is cold, (very). the other one (with the pressure switch on top) is warm.
It looks to me that the pressure is building up because something is blocking the system. To make sure we did open the system and blow air through evaporator to make sure it is not blocked. What should be the pressure at the low side (the port) ? What should I do with it ?
Thanks

Post by **Ozark Lee** » 19 Jul 2013, 18:11

Are the pressures you posted with the compressor running or not? If the compressor is running they are very high. If the compressor is not running they are low. The only numbers that really mean anything are with the compressor running. The static pressure will be all over the place based on the ambient temperature.

A low side pressure of 30 to 40 PSI with the compressor running is within the realm of reality but it depends on the ambient temperature.

...Lee

Post by **taxi** » 08 Aug 2016, 08:08

Hi! It's been a while since I was here last, and I hope I haven't left unfinished business earlier. (such as topics with no solution at the end)

This old topic with evaporator freezing just happened to me too. Long drives only, after about 60-90 minutes the blower starts sounding restricted and airflow diminishes.
After being parked for a while a big puddle of water appears under the car and then everything works perfectly again.

1: Can I check pressure with a tire gauge? It's all I have.
2: Can a faulty low pressure switch cause this?

I have plenty of low pressure switches lying around, it will be easy to try that.
I can take the car to a specialist, but that will cost me. So I would like to begin with cheap possibilities and work my way up.

Thank you for your time!

Post by **abscate** » 08 Aug 2016, 08:59

You can't check AC pressure with a tire gauge reliably.

A bad low pressure switch could cause this trouble but it is not likely.

Post by **taxi** » 08 Aug 2016, 11:04

Thanks for the answer, what do you think is the most common cause for freezing? I have a lot of experience with cars with low charge issues, but have never encountered freezing evaporator as a result.
Maybe I have to suck it up and pay to be sure.