A/C Accumulator Iced Over and Heat Slowly Stops Working

A/C Accumulator Iced Over and Heat Slowly Stops Working

Postby SportsBoy [OP] » December 27th 2020, 5:25am

Ok, so had a two hour drive tonight and it’s about 20* out. Started out plenty warm after the engine heated up, but the strength of the air coming out of the vents slowly decreased until the van was freezing and barely anything was coming out o the vents after 90 minutes or so.
There was still hot air, but even on high barely anything was blowing out. The air did not become cooler, it just slowly stopped blowing.

When we arrived I looked under the hood to see this -
5B4CA152-DC97-4848-8EB8-8C437A354C77.jpeg
Ice city


Seems like my accumulator got into the holiday spirit a bit late or something.

So, I’m pretty confused - not sure why the a/c system would be affected when I had the heater on (not on the a/c setting of course).

The only other thing I could find that was similar is this thread, which was very similar, except the guy was having this issue with his a/c running (which makes way more sense tbh) - https://www.astrosafari.com/viewtopic.php?p=27902

The blower motor and resistor were new this year, the plug is not. All that stuff looked fine though.
The rad and heater core hoses were definitely warm, and the engine temp gauge was at like 180 on the dash, so I don’t think the issue was lack of heat.
I also have eliminated the heater comtrol valves, so no issues there.

I’m wondering if anyone can help me out with why this is happening? I’m going to see what the ac compressor is doing when the hvac controls are going tomorrow, but I don’t even understand how that could be related. I’ll double check the blower motor resistor in the light. Plus I’ll check the a/c relay and low pressure cycling switch as well. Hopefully I find something odd with something, but if not the I’m fully lost.

Thanks folks
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Re: A/C Accumulator Iced Over and Heat Slowly Stops Working

Postby Rod's TrucksRod's Trucks is online! » December 27th 2020, 5:56am

That frost does look very odd, but at 20 degrees I'm not sure it might be somewhat normal when running the A/c.
My guess is that you had the control on DEFROST ( thereby running the A/C). I have seen the outside of the accumulator ice up, under some very cool but humid conditions.
I am wondering if the no/reduced heat output, and the accumulator icing, are two unrelated conditions.
Or, the blend door control is malfunctioning and you just happened to notice the frosty accumulator when you looked under the hood. However, I am not sure why you would have had adequate heat in the beginning.
Others will likely have more ideas/suggestions.
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Re: A/C Accumulator Iced Over and Heat Slowly Stops Working

Postby MechBob » December 27th 2020, 7:20am

LOL,great pics,save them for the future,i would,but being an old guy,dont, know how.I suspect your hi pressure switch is bad.But,as you need to travel tomorrow, just unplug the A/c compressor.
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Re: A/C Accumulator Iced Over and Heat Slowly Stops Working

Postby SportsBoy [OP] » December 29th 2020, 6:02am

Ok, had some time to look at it tonight and learned some things.

Blower motor connections look fine -
2020-12-28 17.25.23.jpg

2020-12-28 17.25.34.jpg


I did a check and the ac compressor runs on all settings except for the upper body only and feet only options on the controls. It runs on this setting, which I didn't realize - is that normal?
2020-12-28 17.54.18.jpg
The two to the right of this one are the ones where the compressor is not engaged


I took apart the lower parts of the dashboard and removed the doghouse - the vacuum lines look good, but it seems that changing the settings doesn't affect where the air is going. I'll have to investigate further.

An interesting discovery was this -
2020-12-28 17.49.55.jpg

There should be a pressure sensor in the back port of the accumulator here, shouldn't there? Like in the purple circle in this picture I found on the internet -
Accum_diagram.jpg

I found the part on Rockauto -
https://www.rockauto.com/en/moreinfo.ph ... 6&jsn=1745

When I added ac to the van in 2019, the system had been partially removed previously. So I guess when the new accumulator went in and there wasn't one of these sensors on the old one, I was none the wiser. The ac was giving us issues after the install though, and to make it work we had to jumper the wire that would normally plug into the sensor. You can see the little orange-ish nub poking out from the wiring behind the accumulator. It makes so much sense now why we had that issue!!! lol

Anyways, more to look at, but could not having that switch freeze up the whole a/c evap coil housing thing and stop up the blower motor perhaps? I dunno, just trying to connect the dots.
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Re: A/C Accumulator Iced Over and Heat Slowly Stops Working

Postby MechBob » December 29th 2020, 7:21am

I will try to explain this simply.the switch on the back of the compressor shuts down the compressor,when the pressure gets "too high".the switch,on the evaporation canister,shuts down the compressor,when the pressure gets too low.Now,as i have seen this is a modified vehicle,do you have the "hi pressure" switch even hooked up? The Hi switch is actually the one that works with the system,to control temps.The "lo" switch is only to keep the compressor from locking up,if all refrigerant is lost.
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Re: A/C Accumulator Iced Over and Heat Slowly Stops Working

Postby AstroWill » December 29th 2020, 7:27pm

SportsBoy wrote:There should be a pressure sensor in the back port of the accumulator here, shouldn't there? Like in the purple circle in this picture I found on the internet -

Yes, that is a problem, install the low pressure switch(aka cycling pressure switch) and hook it up so it works properly. Disconnect your AC compressor(or your bypass) until you do, you can ruin your system like that.

SportsBoy wrote:Anyways, more to look at, but could not having that switch freeze up the whole a/c evap coil housing thing and stop up the blower motor perhaps? I dunno, just trying to connect the dots.

Yes, the low/cycling pressure switch IS freeze protection. Ice forms on the coil and stops the air from flowing through it. Once it thaws then you have airflow again.

Edit: While we are at it, the high pressure switch on the back of the compressor is normally closed and only activated/opened over ~400psi, and it's job is to prevent the relieve valve from popping(spewing oil and refrigerant out of your system).

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Re: A/C Accumulator Iced Over and Heat Slowly Stops Working

Postby N6KB » December 29th 2020, 7:40pm

"the ac compressor runs on all settings except for the upper body only and feet only options on the controls. It runs on this setting, which I didn't realize - is that normal?"

Yes it is normal. In the defrogging modes the A/C compressor is supposed to be on. Defogging works best with dry air. Running air through a cold A/C evaporator precipitates a lot of the water out of the air, drying it. Then it can be heated (or not) depending on the Blue/Red control knob setting, by running it through the heater core.
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Re: A/C Accumulator Iced Over and Heat Slowly Stops Working

Postby SportsBoy [OP] » December 29th 2020, 9:52pm

MechBob wrote:I will try to explain this simply.the switch on the back of the compressor shuts down the compressor,when the pressure gets "too high".the switch,on the evaporation canister,shuts down the compressor,when the pressure gets too low.Now,as i have seen this is a modified vehicle,do you have the "hi pressure" switch even hooked up? The Hi switch is actually the one that works with the system,to control temps.The "lo" switch is only to keep the compressor from locking up,if all refrigerant is lost.

Ok - the switch on the compressor is there I believe, the one on the accumulator is the one missing. Good thing I haven't had a leak - I would have destroyed my new compressor it seems.
AstroWill wrote:
SportsBoy wrote:There should be a pressure sensor in the back port of the accumulator here, shouldn't there? Like in the purple circle in this picture I found on the internet -

Yes, that is a problem, install the low pressure switch(aka cycling pressure switch) and hook it up so it works properly. Disconnect your AC compressor(or your bypass) until you do, you can ruin your system like that.

SportsBoy wrote:Anyways, more to look at, but could not having that switch freeze up the whole a/c evap coil housing thing and stop up the blower motor perhaps? I dunno, just trying to connect the dots.

Yes, the low/cycling pressure switch IS freeze protection. Ice forms on the coil and stops the air from flowing through it. Once it thaws then you have airflow again.

Edit: While we are at it, the high pressure switch on the back of the compressor is normally closed and only activated/opened over ~400psi, and it's job is to prevent the relieve valve from popping(spewing oil and refrigerant out of your system).

Ok, I'll un-jumper that connector so it is disabled. I'll probably grab a new connector from a jy and the switch from rockauto.
Makes sense that you need a switch for pressures too low or high - I just had no idea I was missing one.
N6KB wrote:"the ac compressor runs on all settings except for the upper body only and feet only options on the controls. It runs on this setting, which I didn't realize - is that normal?"

Yes it is normal. In the defrogging modes the A/C compressor is supposed to be on. Defogging works best with dry air. Running air through a cold A/C evaporator precipitates a lot of the water out of the air, drying it. Then it can be heated (or not) depending on the Blue/Red control knob setting, by running it through the heater core.


I get that it runs on defrost, and on the a/c settings, I just didn't think that the setting it is on in the picture (the one with air blowing at you from the upper and lower vents simultaneously) was air conditioning too.
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Re: A/C Accumulator Iced Over and Heat Slowly Stops Working

Postby AstroWill » December 29th 2020, 10:12pm

SportsBoy wrote:I get that it runs on defrost, and on the a/c settings, I just didn't think that the setting it is on in the picture (the one with air blowing at you from the upper and lower vents simultaneously) was air conditioning too.

Heater and vent positions are the only two where the AC compressor won't turn on.
If you have an owners manual it's on page 3-3, if you don't have one you can get a PDF here: https://www.astrosafari.com/viewforum.php?f=110

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Re: A/C Accumulator Iced Over and Heat Slowly Stops Working

Postby Leeann_93 » December 30th 2020, 3:42am

You can see the line that shows you that setting (floor and dash vents) is AC. GM used to call it “Bilev”.

The AC compressor runs on all settings except floor only or dash vents only. It’s designed that way
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Re: A/C Accumulator Iced Over and Heat Slowly Stops Working

Postby SportsBoy [OP] » December 31st 2020, 4:44am

Leeann_93 wrote:You can see the line that shows you that setting (floor and dash vents) is AC. GM used to call it “Bilev”.

The AC compressor runs on all settings except floor only or dash vents only. It’s designed that way

AstroWill wrote:
SportsBoy wrote:I get that it runs on defrost, and on the a/c settings, I just didn't think that the setting it is on in the picture (the one with air blowing at you from the upper and lower vents simultaneously) was air conditioning too.

Heater and vent positions are the only two where the AC compressor won't turn on.
If you have an owners manual it's on page 3-3, if you don't have one you can get a PDF here: https://www.astrosafari.com/viewforum.php?f=110

Thanks guys! I spent a long time looking in the fsm for exactly what each selection on the hvac control knob does, but didn't even think to look in the owner's manual :whack:

In other news, I checked out everything and it seems like everything is fine (minus the switch being missing). Drove 2 hours in the van with supah hot heat tonight.

Checked all fuses, a/c relay, vacuum hoses, vacuum check valve, blend door and temp control motor, grounds, and I think that's it.
Found one ground that was undone, by the driver's rear wheel well. I don't think that was causing any issues though. Seems like the freezing over of the blower housing must have been the issue! :rockon:
2020-12-30 16.03.18.jpg
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Re: A/C Accumulator Iced Over and Heat Slowly Stops Working

Postby AstroWill » January 5th 2021, 2:20am

SportsBoy wrote:In other news, I checked out everything and it seems like everything is fine (minus the switch being missing). Drove 2 hours in the van with supah hot heat tonight.
Seems like the freezing over of the blower housing must have been the issue! :rockon:


Awesome man! Let us know how it goes once you have the switch installed.

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Re: A/C Accumulator Iced Over and Heat Slowly Stops Working

Postby SportsBoy [OP] » January 10th 2021, 5:12am

Got the switch and wiring in there today - we'll see how it does when it is driving again.
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