Advice on McQuay R-410A MHC Standard Range & MHW Geothermal
I'm not a tech, I'm a homeowner. We purchased an apartment in NYC and one of the conditions on closing was that the building install 4 new PTAC units that were thermostatically controlled (vs. the PTAC units that were already installed that just have on/off, hi/lo, hot/cold)
The units they chose were McQuay R-410A MHC Standard Range & MHW Geothermal. We've had nothing but a string of problems. One unit was pulled immediately to have the compressor replaced. Another one had a drain issue that caused water damage on the floor. A third would randomly blow heat during the summer and now doesn't turn on at all (they've ordered a new thermostat/receiver and expect it in 4-5 weeks).
My question though is with the 3 units that do turn on. Please someone tell me if this is normal. Here's what happens.
Come in to cold apartment (low 60s).
Set thermostat to 70.
Fan comes on.
Compressor comes on blowing warm air.
Room heats to set point of 70.
Unit turns off.
Wait for temperature on thermostat to drop below set point
Fan on unit comes on
Compressor comes on blowing COLD air
temperature continues to drop
Once temperature has dropped 2-3 degrees the compressor goes off
Fan stays on
Compressor comes back on blowing warm air
This doesn't seem normal, but every time someone tests it, they just turn the temperature up 4 degrees, the heat comes on and they claim it works. They are coming back on Thursday and I'm hoping I can have them stick around to see the problem.
Thank you for any advice you can provide.
Here's a video of the problem. Im not sure you can hear the unit or not but I'm holding the thermostat in front of one of the units and you can watch the temperature drop for about 6 minutes before the heat comes on. The compressor kicks on 15 seconds into the video and runs until 3:18 or so.The fan continues to run and then around 3 minutes later the heat kicks on.
I'm thinking soemone needs oto watch in run multiple cycles. Almost soudns liek its' overshooting, going itno cooling mode, then switching back to heating again. WHere is the thermostat located in relationship ot the system? Looke liek a wireless thermostat.
Try taking it out of "auto" mode for heating and cooling. I notice it does show heating mode however. I'm tinking it didnt; chage the reversing valve for soem reason.
Might also try testing it with a wired thermostat.
Thanks for replying. The thermostats are wireless. I've tried various places around the room, usually we keep it on the opposite side of the room where the unit can't blow directly on it. In the video I was right in front of the unit so you could hopefully hear the compressor and the changes in sound.
There is a different thermostat for each unit. There is no "auto" setting, just heat, cool, or off. The only auto is for the fan mode.
I'm not sure the thermostat is the problem since I have 4 units and 3 of them do this (the 4th isn't working at all right now).
When you come home and goose up the temp to 70, the electric heat is warming you back up. When it soon drops below 70, it turns on the compressor for heating and sounds like something isn't working. Reversing valve stuck in cool or something. Is this unit a PTAC or water source heat pump?
They are water source heat pumps (I wasn't sure, but pulled out the installation booklet left by the installers).
Originally Posted by BaldLoonie
Why would the reversing valve be stuck on all the units?
Well at least I know one thing, this isn't how it should be working.
Probably got wired up wrong.
That's kind of been my feeling. The installers brushing me off for a while does not give me confidence in their work. Nor does the installer telling me "we're just plumbers". Considering the fact they didn't get the drain right on one of the units, I would not be surprised if the units are not installed correctly.
Thank you everyone for your help. While I can't fix the problem, you've at least made me confident that there is indeed a problem and I'm not crazy to think so.
So the McQuay tech just came and went. He was here 30 min. late and stayed about 20 min. When he walked in, one of the units was blowing cold. Before he left he witnessed all three blowing cold. One unit had the heat on immediately when he set the thermostat. Then when it went on automatically (2-3 minutes after it had shut off) it blew the a/c.
He's trying to tell me that the problem has to be the buildings water because all three units are acting the same way. He said the wiring is done at the factory and is correct. The only thing he did as a test was to test the current on ONE wire. I tried to explain that the 3 minutes that one unit was off between cycles was not enough for the water to cool down. I also explained that if the temperature difference is greater than 1-2 degrees it will turn on heat right away no problem (if the room is 65 and I set it to 70). He still insists it's the water and wants to take a unit out to test at the shop for 3-4 days.
That would put me down 2 units out of 4. Can anyone help? Can you get me a number or email contact at McQuay headquarters I can call to try to get someone to listen to the actual problem? I'm at my wits end with the building, the installer, and now the local manufacturers representatives.
What are the water temps on the buildign loop?
We ran into this recently at my work. Long story short, we use city water in a open loop and the incomming water temp is 38F. Our larger Trane package units will tolerate it, but thsi smaller carrier residental/light commercial unit locks out on freeze protection. The same coudl be happeneing to your. The old units could run down to maybe 40F, the new ones might require 45F without antifreeze . IF thsi is the issue, the installing contractor should have noticed this. THe building operator might run the boiler just enough ot maintain 40F and no more.
Post the water temps if you can. Maybe you can drain some into a cup and stick a little pocket kitchen digital thermometer in it.
IT is interestign the 2 out of 4 work fine. Are they the same model.
SOrry, but hte contractor sucks. he left without fixing hte issue ot recommending how to fix it or what ot tell you buiding manager. What does your building manager have to say?
Is it blowing COLD (in cooling mode) or is it just blowing room air?
motoguy128 - None of the units are working fine. I have 4 units. 1 doesn't work at all (4-5 wks for new receiver), and if they take another to test I'll have 2 that are acting the same way. The building manager says the water temp is 75F, which is just above the normal water range in the installation book.
BaldLoonie- It is blowing COLD not just room air. When the thermostat temperature drops below the set point the fan comes on (just room air) then you hear the compressor come on and the air gets very cold. About 3 minutes later (after the temperature has dropped another 2-3 degrees) the compressor goes off (back to just room air) and then you hear the heat come on and warm air comes out.
Somewhere I remember reading that the fan has two speeds. One speed kicks in when the temperature difference is slight and the other speed kicks in when there is a greater difference. Here’s my theory. When the thermostat is set to heat and the first speed kick in the unit for some reason is triggering the A/C and not the heat. Then, when the temperature difference is great enough it triggers the heat correctly.
SOUNDS LIKE it is coming on in cool mode and when the stat drops a bit, it brings on electric heat instead and you finally get heat. When it is heating, do you hear the compressor running? Do you hear a woosh as the reversing valve switches to heat?
I'll research a bit more later. Trying to find setup manual for that wireless thermostat.
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