Volvo 2000 S70 - a/c will run fine but then blow hot

[ZanyZonie]

Hi,

This is my first post. My a/c will run fine but then blow hot out of the two driver's side vents; then it will run fine again; sometimes I'll play around with switching from recirc to fresh air but I am not sure this makes any difference. This issue has occurred on several occasions over the 3 years I have owned the car. I trust my mechanic, who I have gone to for years (I previously owned the same make, model and year until it was totaled and had purchased it new); my mechanic is Volvo certified.

Work that has been done on the a/c:

1. June 2015: New compressor assembly; replaced O rings and charged system. (The fan had not worked at all prior to this service.)

2. September 2016: Complete a/c service; system was put into a vacuum for 30 min and recharged. (The hot air was blowing out of the two driver's side vents prior to this service.)

3. March 2017: Blower fan, blower motor resistor, blower motor assembly. (The fan had not been blowing at times and was not blowing at full strength when it did blow.)

4. May 19, 2017: A/C was recharged. (The hot air was blowing out of the two driver's side vents prior to this service.) My mechanic said there was possibly a leak in the evaporator and that it would make sense to recharge the a/c once a year rather than spend $2,000 on a new evaporator.

After this service 3 days ago the hot air has continued to blow. My mechanic now believes it is the compressor. Before I go ahead with this work, I would love to hear from anyone familiar with this issue who could offer advice on a solution. The only information I could find was that the compressor may need to be shimmied or de-shimmied (whatever that means

Note that I am a complete layperson when it comes to this stuff.

Thank you in advance for your help,

Debbie

[abscate]

Welcome Debbie!

The evaporator is a known 'weak point' on these cars but in your hot dry climate I think they last a lot longer than in humid climates.

Are you getting cold air out of one side but not the other? If you get cold air anywhere, we should put aside the evaporator for now.

The damper motor (a small motor under the dash) sends the air to the right side as well as selects the temp - if that goes bad then you will get the air in the wrong place. A code reader should give the fault though - a Volvo guy/gal can read the code and tell you if the fault is there.

My mechanic said there was possibly a leak in the evaporator and that it would make sense to recharge the a/c once a year rather than spend $2,000 on a new evaporator.

They should send people who give this advice out into the desert to die from UV exposure slowly. Seriously, this CFC are bad for the planet and belong in your AC system, sealed up correctly, not getting blown off to save some green. $2000 is a bit pricy for an evap replacement. I think it is a 10 hour job in all data but should be doable in less. To be clear, the advice isn't 'wrong' I just don't agree with that philosophy on AC.

The shimming story

Your serpentine (fan belt) turns the wheel on the compressor AC, but the compressor only turns when commanded by you turning on the AC. When the command comes, a magnet pushes another plate against the turning wheel which then turns the compressor. The gap between the wheels is important. Over time it wears until the magnet can no loner pull the plates together. You then lose your cold air as the system does not respond to the command for cold air, even though all the pumps and refrigerants are all there.

The cheap fix here is called the 'bread clip' or 'zip tie' fix.

[ZanyZonie]

Thank you for your prompt reply!

In answer to your question, there is cold air coming out of the two passenger side vents; that side does not appear to get warm. It is the two driver's side vents that go back-and-forth on the temperature; sometimes it blows cold; sometimes it blows hot.

Forgive me in advance for asking these questions but I want to make sure I understand...

So I think what I am gathering from your post is that it is not the evaporator. And it isn't the damper motor because the air going to the right side is cold, is that correct?

And the shimmy thing could be the issue? Or would there be no cold air on either side if this were the cause?

What is the "bread clip" or "zip tie" fix? Is that part of the shimmy thing?

And my mechanic should be able to tell exactly what is wrong by the code reader?

Thank you again,

Debbie

[abscate]

The cold air is telling you that the refrigerant part of the system is working ok. The difference between the passenger side and driver side is telling you the damper isn't working right, as long as you have the two sides set to the same temperature.

THere should be a code set in the climate system that a good code reader can pick up - the cheap one or generic ones cant read these VOLVO climate codes, but the Volvo guy should have one that will.

The bread clip fix is correcting a non-functioning comporessor clutch, but we have ruled that out. When the clutch fails, you get no cold air anywhere. WHen the evaporator fails, you get no cold air.

Congrats - you have managed to have failure in the cheapest part of the system!

[abscate]

There are a four motors in your climate system -

One decides if the air comes from inside and outside - the RECIRC door
One set directs the air between floor, dash, or windshield
Two more 'blend doors' mix the heated air and the AC air to set the temperature on the right and left side.

As you might guess - your symptom points to the driver side blend Door as the problem.

[ZanyZonie]

Thank you again! I copied parts of your messages (not the part about the desert and emailed them to my mechanic.

One thing I forgot to mention is that the fan isn't blowing as strong from the 2 driver's side vents; especially when the air is hot. Does this change any of the possibilities of what might be wrong?

[abscate]

I'm guessing here but that could be something blocking the damper door, like a piece of weatherstripping ? That would explain why it's intermittent , and the change in flow.

There is only one blower motor so the difference in flow is noteworthy. It is tough to gauge flow by hand though, the temp differential fools you.

[ZanyZonie]

I cannot thank you enough. I just sent that additional information to my mechanic. I will let you know how things go.

Debbie