View Full Version : Dual Speed Operation Question
I'm a homeowner with a few questions about my HVAC system. Sorry if I don't have the terms down properly :o
The system is a 3-year old Bryant HP/Gas system, handling about 3000 square feet in the Kansas City Area. The stat is a 5+2 day programmable, dual-mode, automatic unit.
Question 1: is it normal for the blower to reduce speed for A/C actuation? Heat and "Fan Only" run at full speed, but A/C is reduced.
Why I ask: I had techs out 3 times for failure to properly install and charge the system. As you know, the condenser became a block of ice until they detected a faulty coupling install.
The Problem: In the summer months, the system has a tough time cooling the house (consistently runs from afternoon to bedtime). I'm not sure of the tonnage, but I can pull the panel on the compressor to find out. If the blower speed should be at full power for cooling, I suppose I would need to have a tech adjust that.
Question 2: Of course this is a very inefficient "builder's grade" system, and the utility bills are rather high. Would it make sense to have someone install an intake runner in the basement to draw cool air for summer (with a damper of some sort for Winter)? I have the vents and output sections adjusted for the rarely used rooms and hot spots. The flat, backside of the house faces West, which is also a challenge.
My expertise is in vehicle fuel economy -- so I'm a bit lost with HVAC. I'm a moderator over at the EcoModder.com (http://ecomodder.com) Forums -- perhaps I can help return the favor for anyone looking for advice on saving fuel.
Thanks in advance...
05-18-2008, 11:22 AM
Don't need to pull the panel cover, just post the model number.
They apparently have teh blower set to a slower speed for cooling.
Should have them adjust it to teh proper speed(might already be right) and teh system charge rechecked at teh new speed.
05-18-2008, 11:27 AM
There are a few occasions when cooling should be on a lower speed than heating. Usually happens in the north where a big furnace is needed but a small A/C. Few installers bother to set blower speeds, they just leave them where they come from the factory but we find we do call for low for cool at times after consulting the blower charts and checking duct pressure.
In the Kansas City area, the temps range from -5F to 105F and the full range of humidity. The gas burner does a great job (but the AFUE rating nearly sets the benchmark for "Least Efficient"). The HP does the trick during that rare temp range of operation.
The system: HP Bryant Model# 661CJ04-G and the burner is the "Plus 80" for reference. Can you tell the tonnage from the model?
It sounds like someone needs to check the speeds. When we moved in, they didn't have the Stat hooked up, so it was a rush job -- perhaps they didn't run the checklist.
Again, much appreciated!
05-18-2008, 06:41 PM
When you say "the system has a tough time cooling the house (consistently runs from afternoon to bedtime)" do you mean the house doesn't reach the set point of the thermostat or just that it runs consistantly? How far from the stat setting is it running on low speed? If you lower the stat to 5-10* below the house temp. does it change?
I'm hoping it's a multi/variable speed blower but sounds like it may just be single. Having the blower run slower while on AC will remove more humidity but it sounds like the unit may not be meeting your stats set point and could be as simple as a mis wired thermostat.
To answer your question, the A/C struggles to reduce the temp to the setpoint.
When the high blower speed starts, the return duct pressure pulls on the duct side and makes a "bang" sound -- this way I know it's at full speed. (could this indicate poor air return capacity?)
Anyways, I got bold with the whole works and popped the blower cover (cut the power and all that). The high-speed blower wire was hooked to the "cool" side of the relay and the blue (Med-Lo) wire to the heat connector. What puzzles me is that the red (Lo) wire is hooked to the constant fan relay, but runs at full speed when selected. Everything was checked, and is wired to factory spec, so it must be the board or Stat making that decision. I made sure to the others were parked securely.
I came back and read about the faulty Stat (thanks Daltex!) This is a dual-stage unit so I started racking my brain on what could fix it.
I recalled seeing a dual speed dipswitch on the Stat. I took a chance on switching it to "Dual Stage". After fooling with it most of the evening, this tiny switch finally did the trick!
After the compressor rested-up, it kicked on, the blower spooled-up and Bang! Full power.
Now, we'll see if it helps with cooling the place properly. If not, it's back to square-1. I guess the humidity may suffer a bit, but airflow is the biggest problem. Some vents barely had any flow in the far end of the house.
I understand this isn't a DIY forum, so apologies to anyone that may take offense to the self-repair. :o
05-19-2008, 09:49 AM
Thats strange or maybe Im not understanding the situation. In your first post you said it was builder grade equipment. If so I dont think you have a 2 speed compresor. The way you described blower speed I dont think you even have a variable speed blower. I think you may have dual fuel, HP with gas backup.
If this is correct I dont think your problem is solved. The switch you are talking about would not change the signal the t-stat sends the airhandler for cooling.
Could someone take the time to explain why Im wrong, if Im wrong. Thanks.
05-19-2008, 10:35 AM
The 661 is a low end 10 SEER pump. The Plus 80 is most likely the standard 80 with standard 4 speed PSC motor.
That's where I think the mix up is: "Dual-Speed". Does that commonly refer to the compressor?
The problem has returned. The fan blower is at full speed, but kicks down to medium-low when the A/C compressor engages.
I ran the black blower motor wire to the "Heat" side, thinking that the relay had something to do with fan speed. I'm thinking the board is determining speed, or the Stat -- I don't know for sure.
The system worked perfectly at full speed. The house cooled properly and it pulled quite a bit of humidity, judging by the drain flow from the condenser.
The only change since then: I ran the blower for a while this morning to circulate/filter the air.
All I want is full blower fan during A/C and it's driving me nuts (and running a long time) = $$$.
Would it help if I posted the schematic? The Red (low) wire is plugged into the constant-blower SPDT relay (per factory spec) -- with the black (hi) on the heat side of the heat/cool relay (experimenting). It worked when I flipped the dual-speed dipswitch to "On". Should I reset the sysem and repeat the procedure and not touch the fan button?
Do you think it's the board or the Stat controlling the fan speed (It's a BBPDF...so dual-fuel, outdoor temp).
05-19-2008, 06:39 PM
You need a tech to come out and figure it out.
05-19-2008, 06:50 PM
The stat tells the board to tell the motor what to do :D
Yeah, I think I'm to that point...
My Wife already referenced the Dad from the "Christmas Story" movie.
It's a clinker! That blasted stupid furnace dadgummit!
Thanks for the effort fellas...
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